diff --git a/src/commands/signup.ts b/src/commands/signup.ts
index 746437d..01c7d21 100644
--- a/src/commands/signup.ts
+++ b/src/commands/signup.ts
@@ -29,6 +29,13 @@ export default class Signup extends BaseCommand {
       char: 'n',
       description: 'Your name (skips interactive prompt during signup)',
     }),
+    ref: Flags.string({
+      description:
+        'Referral token from linqapp.com, used to connect this signup to the site visit that led to it. Populated automatically when the quickstart is copied from https://linqapp.com/cli.',
+      // Not a user-facing knob — it only ever arrives pre-filled in a copied
+      // command, and surfacing it in `--help` invites confusion.
+      hidden: true,
+    }),
   };
 
   async run(): Promise<void> {
@@ -82,6 +89,7 @@ export default class Signup extends BaseCommand {
       email,
       code: flags.code?.trim(),
       name: flags.name?.trim(),
+      ref: flags.ref?.trim(),
       log: (msg) => this.log(msg),
       exit: (code) => this.exit(code),
       parseError: (res) => this.parseError(res),
diff --git a/src/lib/auth-flow.ts b/src/lib/auth-flow.ts
index 40ca9a3..f786c61 100644
--- a/src/lib/auth-flow.ts
+++ b/src/lib/auth-flow.ts
@@ -21,6 +21,11 @@ interface AuthFlowOptions {
   // so `linq signup` is fully scriptable / AI-agent driven.
   code?: string;
   name?: string;
+  // Opaque referral token minted by linqapp.com and baked into the copied
+  // quickstart. Forwarded verbatim; the backend decides whether it is still
+  // valid. Nothing here depends on its format, so a stale or malformed value
+  // costs nothing beyond losing attribution for this signup.
+  ref?: string;
   log: (msg: string) => void;
   exit: (code: number) => never;
   parseError: (res: Response) => Promise<string>;
@@ -42,7 +47,15 @@ export async function checkExistingSession(): Promise<string | null> {
 }
 
 export async function runAuthFlow(opts: AuthFlowOptions): Promise<void> {
-  const { email, code: codeFlag, name: nameFlag, log, exit, parseError } = opts;
+  const {
+    email,
+    code: codeFlag,
+    name: nameFlag,
+    ref: refFlag,
+    log,
+    exit,
+    parseError,
+  } = opts;
 
   // Step 1: Send OTP.
   // Skipped entirely when `--code` was passed — the caller already has a
@@ -207,7 +220,13 @@ export async function runAuthFlow(opts: AuthFlowOptions): Promise<void> {
       const signupRes = await fetch(`${BACKEND_URL}/cli/signup`, {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
-        body: JSON.stringify({ signupToken: verifyResult.signupToken, name }),
+        body: JSON.stringify({
+          signupToken: verifyResult.signupToken,
+          name,
+          // Omitted entirely when absent so the payload is unchanged for
+          // anyone who did not arrive via a copied quickstart.
+          ...(refFlag ? { webDistinctId: refFlag } : {}),
+        }),
       });
 
       if (!signupRes.ok) {
diff --git a/test/commands/signup.test.ts b/test/commands/signup.test.ts
index dbc6d43..80ef29d 100644
--- a/test/commands/signup.test.ts
+++ b/test/commands/signup.test.ts
@@ -131,4 +131,81 @@ describe('signup (email OTP flow)', () => {
     // Should never have prompted for a code
     expect(mockInput).not.toHaveBeenCalled();
   });
+
+  // --ref carries the visitor's linqapp.com PostHog id across the gap between
+  // the browser and the terminal. It arrives pre-filled in the quickstart
+  // copied from the CLI page and is forwarded verbatim to /cli/signup, where
+  // the backend aliases the anonymous site history onto the new account.
+  function signupBody() {
+    const call = mockFetch.mock.calls.find((c) =>
+      (c[0] as string).endsWith('/cli/signup')
+    );
+    return JSON.parse((call![1] as RequestInit).body as string);
+  }
+
+  // Both --ref tests run fully non-interactively (--email --code --name),
+  // which skips send-otp entirely: re-sending would mint a fresh OTP and
+  // invalidate the code being verified. So only verify-code and signup are
+  // mocked here.
+  function mockNonInteractiveSignupFlow() {
+    mockFetch
+      .mockResolvedValueOnce(
+        jsonResponse(200, {
+          needsSignup: true,
+          signupToken: 'sgn-tok-1',
+          email: 'new@example.com',
+        })
+      )
+      .mockResolvedValueOnce(
+        jsonResponse(201, {
+          token: 'api-token-xyz',
+          orgId: '1234',
+          email: 'new@example.com',
+          name: 'Test User',
+          accountInfo: {
+            accountLabel: 'Shared',
+            phones: [{ phoneNumber: '+12025551234' }],
+          },
+        })
+      );
+  }
+
+  it('forwards --ref to /cli/signup as webDistinctId', async () => {
+    mockNonInteractiveSignupFlow();
+
+    const config = await Config.load({ root: process.cwd() });
+    const cmd = new Signup(
+      [
+        '--email',
+        'new@example.com',
+        '--code',
+        '123456',
+        '--name',
+        'Test User',
+        '--ref',
+        '0198f2a1-dead-beef-cafe-000000000000~1780000000',
+      ],
+      config
+    );
+    await cmd.run();
+
+    expect(signupBody().webDistinctId).toBe(
+      '0198f2a1-dead-beef-cafe-000000000000~1780000000'
+    );
+  });
+
+  it('omits webDistinctId entirely when --ref is absent', async () => {
+    mockNonInteractiveSignupFlow();
+
+    const config = await Config.load({ root: process.cwd() });
+    const cmd = new Signup(
+      ['--email', 'new@example.com', '--code', '123456', '--name', 'Test User'],
+      config
+    );
+    await cmd.run();
+
+    // Absent, not null/empty — the payload must be byte-identical to what
+    // pre-2.6.0 clients send for anyone who did not arrive via the quickstart.
+    expect('webDistinctId' in signupBody()).toBe(false);
+  });
 });