diff --git a/excalidraw-app/components/AtprotoCreateAccountDialog.tsx b/excalidraw-app/components/AtprotoCreateAccountDialog.tsx
new file mode 100644
index 00000000..5b5c5fe6
--- /dev/null
+++ b/excalidraw-app/components/AtprotoCreateAccountDialog.tsx
@@ -0,0 +1,93 @@
+import { Dialog } from "@excalidraw/excalidraw/components/Dialog";
+import { FilledButton } from "@excalidraw/excalidraw/components/FilledButton";
+import { useState } from "react";
+
+import { createAccount } from "../data/atproto/client";
+
+/**
+ * Deliberate speed bump in front of account creation: an Atmosphere identity is
+ * shared across every atproto app, so most people asking for a new account
+ * already have one and would only fragment their data by making a second.
+ */
+export const AtprotoCreateAccountDialog = ({
+  onCancel,
+}: {
+  onCancel: () => void;
+}) => {
+  const [isRedirecting, setIsRedirecting] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  const onConfirm = async () => {
+    if (isRedirecting) {
+      return;
+    }
+    setIsRedirecting(true);
+    setError(null);
+    try {
+      // redirects away on success; local drawing is preserved via LocalData
+      await createAccount();
+      // reaching this point means the user navigated back / aborted
+      setIsRedirecting(false);
+    } catch (error: any) {
+      console.error(error);
+      setError(error.message);
+      setIsRedirecting(false);
+    }
+  };
+
+  return (
+    <Dialog
+      size="small"
+      onCloseRequest={onCancel}
+      title="Wait — do you already have one?"
+    >
+      <div className="AtprotoCreateAccountDialog">
+        <div className="AtprotoCreateAccountDialog__body">
+          <p>
+            An Atmosphere account isn't specific to Lexidraw. It's the same
+            account you use for{" "}
+            <a href="https://bsky.app" target="_blank" rel="noreferrer">
+              Bluesky
+            </a>
+            ,{" "}
+            <a href="https://tangled.org" target="_blank" rel="noreferrer">
+              Tangled
+            </a>
+            ,{" "}
+            <a href="https://stream.place" target="_blank" rel="noreferrer">
+              stream.place
+            </a>
+            ,{" "}
+            <a href="https://leaflet.pub" target="_blank" rel="noreferrer">
+              leaflet.pub
+            </a>
+            , and{" "}
+            <a href="https://atstore.fyi" target="_blank" rel="noreferrer">
+              more
+            </a>
+            . If any of those are yours, go back and sign in with that handle
+            instead.
+          </p>
+          <p>
+            Still need one? We'll send you to <code>selfhosted.social</code> to
+            sign up, then bring you back here.
+          </p>
+        </div>
+        {error && <p className="AtprotoCreateAccountDialog__error">{error}</p>}
+        <div className="AtprotoCreateAccountDialog__actions">
+          <FilledButton
+            size="large"
+            variant="outlined"
+            label="I already have one"
+            onClick={onCancel}
+          />
+          <FilledButton
+            size="large"
+            label={isRedirecting ? "Redirecting…" : "Create an account"}
+            onClick={onConfirm}
+          />
+        </div>
+      </div>
+    </Dialog>
+  );
+};
diff --git a/excalidraw-app/components/AtprotoSignInDialog.scss b/excalidraw-app/components/AtprotoSignInDialog.scss
new file mode 100644
index 00000000..eed7f621
--- /dev/null
+++ b/excalidraw-app/components/AtprotoSignInDialog.scss
@@ -0,0 +1,61 @@
+.excalidraw {
+  .AtprotoSignInDialog {
+    display: flex;
+    flex-direction: column;
+    gap: 1rem;
+
+    &__intro {
+      margin: 0;
+    }
+
+    &__error {
+      margin: 0;
+      color: var(--color-danger);
+    }
+
+    &__create {
+      display: flex;
+      flex-direction: column;
+      gap: 0.75rem;
+
+      padding-top: 1rem;
+      border-top: 1px solid var(--dialog-border-color);
+      font-size: 0.875rem;
+      line-height: 150%;
+
+      p {
+        margin: 0;
+      }
+    }
+  }
+
+  .AtprotoCreateAccountDialog {
+    display: flex;
+    flex-direction: column;
+    gap: 1.5rem;
+
+    &__body {
+      display: flex;
+      flex-direction: column;
+      gap: 0.75rem;
+
+      font-size: 0.875rem;
+      line-height: 150%;
+
+      p {
+        margin: 0;
+      }
+    }
+
+    &__error {
+      margin: 0;
+      color: var(--color-danger);
+    }
+
+    &__actions {
+      display: flex;
+      justify-content: flex-end;
+      gap: 0.75rem;
+    }
+  }
+}
diff --git a/excalidraw-app/components/AtprotoSignInDialog.tsx b/excalidraw-app/components/AtprotoSignInDialog.tsx
index 29549cf5..818b6e73 100644
--- a/excalidraw-app/components/AtprotoSignInDialog.tsx
+++ b/excalidraw-app/components/AtprotoSignInDialog.tsx
@@ -8,6 +8,10 @@ import { useState } from "react";
 import { atom, useAtom } from "../app-jotai";
 import { signIn } from "../data/atproto/client";
 
+import { AtprotoCreateAccountDialog } from "./AtprotoCreateAccountDialog";
+
+import "./AtprotoSignInDialog.scss";
+
 export const signInDialogOpenAtom = atom(false);
 
 export const AtprotoSignInDialog = () => {
@@ -15,6 +19,7 @@ export const AtprotoSignInDialog = () => {
   const [handle, setHandle] = useState("");
   const [isRedirecting, setIsRedirecting] = useState(false);
   const [error, setError] = useState<string | null>(null);
+  const [showCreateConfirm, setShowCreateConfirm] = useState(false);
 
   if (!isOpen) {
     return null;
@@ -45,8 +50,8 @@ export const AtprotoSignInDialog = () => {
       onCloseRequest={() => setIsOpen(false)}
       title="Sign in"
     >
-      <div style={{ display: "flex", flexDirection: "column", gap: "1rem" }}>
-        <p style={{ margin: 0 }}>
+      <div className="AtprotoSignInDialog">
+        <p className="AtprotoSignInDialog__intro">
           Enter your Atmosphere handle (e.g. <code>alice.bsky.social</code>) to
           sign in with atproto. Your drawings are saved to your own account.
         </p>
@@ -58,16 +63,28 @@ export const AtprotoSignInDialog = () => {
           onChange={setHandle}
           onKeyDown={(event) => event.key === KEYS.ENTER && onSubmit()}
         />
-        {error && (
-          <p style={{ margin: 0, color: "var(--color-danger)" }}>{error}</p>
-        )}
+        {error && <p className="AtprotoSignInDialog__error">{error}</p>}
         <FilledButton
           size="large"
           label={isRedirecting ? "Redirecting…" : "Sign in"}
           icon={loginIcon}
           onClick={onSubmit}
         />
+        <div className="AtprotoSignInDialog__create">
+          <p>Don't have an Atmosphere account?</p>
+          <FilledButton
+            size="large"
+            variant="outlined"
+            label="Create an account"
+            onClick={() => setShowCreateConfirm(true)}
+          />
+        </div>
       </div>
+      {showCreateConfirm && (
+        <AtprotoCreateAccountDialog
+          onCancel={() => setShowCreateConfirm(false)}
+        />
+      )}
     </Dialog>
   );
 };
diff --git a/excalidraw-app/data/atproto/client.ts b/excalidraw-app/data/atproto/client.ts
index ee477f10..9b71172a 100644
--- a/excalidraw-app/data/atproto/client.ts
+++ b/excalidraw-app/data/atproto/client.ts
@@ -7,6 +7,8 @@ import {
   extractAtprotoData,
 } from "@atproto/oauth-client-browser";
 
+import { SIGNUP_PDS } from "./constants";
+
 import type { OAuthSession } from "@atproto/oauth-client-browser";
 
 // Both the scene record and its revision checkpoints need repo write scope.
@@ -101,6 +103,19 @@ export const signIn = async (handle: string): Promise<void> => {
   await client.signInRedirect(handle, { scope: OAUTH_SCOPE });
 };
 
+/**
+ * Redirects to SIGNUP_PDS's account creation flow; never resolves on success.
+ * An input starting with https:// is resolved as a PDS URL rather than as a
+ * handle, and prompt "create" asks that server for its sign-up screen.
+ */
+export const createAccount = async (): Promise<void> => {
+  const client = await getOAuthClient();
+  await client.signInRedirect(SIGNUP_PDS, {
+    scope: OAUTH_SCOPE,
+    prompt: "create",
+  });
+};
+
 export const signOut = async (did: string): Promise<void> => {
   const client = await getOAuthClient();
   await client.revoke(did);
diff --git a/excalidraw-app/data/atproto/constants.ts b/excalidraw-app/data/atproto/constants.ts
index 6db6e953..caa2de06 100644
--- a/excalidraw-app/data/atproto/constants.ts
+++ b/excalidraw-app/data/atproto/constants.ts
@@ -8,3 +8,6 @@ export const SCENE_BLOB_WARN_BYTES = 10 * 1024 * 1024;
 
 // debounce interval for autosaving the active drawing to the PDS
 export const SAVE_TO_PDS_TIMEOUT = 15000;
+
+// PDS offered for in-app account creation; passed to OAuth as a service URL
+export const SIGNUP_PDS = "https://selfhosted.social";