diff --git a/docs/buzz-help.md b/docs/buzz-help.md
index 964380f44c..56e3c3700c 100644
--- a/docs/buzz-help.md
+++ b/docs/buzz-help.md
@@ -72,6 +72,9 @@ the interface unless an available tool actually supports that action.
   unavailable until you sign in. Sign-in, sign-out and when the current
   sign-in ends also live under
   **Settings → Buzz → Identity → Organization sign-in**.
+- When a community requires organization sign-in, the sidebar or join dialog
+  explains why and offers **Sign in with** the organization’s name or server
+  address. Complete sign-in to reconnect; in the join dialog, choose **Continue**.
 - Signed in to more than one organization server? **Organization sign-in**
   lists each one you're signed in to, with the communities it's used by, and
   each **Sign out** ends only that server's sign-in. Your organization's own
diff --git a/src/app/shell/PrimarySidebar.sign-in.test.tsx b/src/app/shell/PrimarySidebar.sign-in.test.tsx
index 4334c97142..b60d433e54 100644
--- a/src/app/shell/PrimarySidebar.sign-in.test.tsx
+++ b/src/app/shell/PrimarySidebar.sign-in.test.tsx
@@ -60,11 +60,18 @@ it("offers explicit sign-in when the live socket refuses a protected community",
   const h = await refusedLive("Federated sign-in is required");
   // The cached channel list stays; nothing signs in on its own.
   expect(screen.getByRole("button", { name: "Chats" })).toBeVisible();
+  expect(
+    await screen.findByText(
+      "This community requires builderlab.example sign-in.",
+    ),
+  ).toBeVisible();
   expect(h.identity.service.signIn).not.toHaveBeenCalled();
   expect(h.connects()).toBe(1);
-  await userEvent
-    .setup()
-    .click(await screen.findByRole("button", { name: "Sign in" }));
+  await userEvent.setup().click(
+    await screen.findByRole("button", {
+      name: "Sign in with builderlab.example",
+    }),
+  );
   expect(h.identity.service.signIn).toHaveBeenCalledOnce();
   // A completed sign-in reconnects the live socket with the new session.
   await waitFor(() => expect(h.connects()).toBe(2));
@@ -76,7 +83,9 @@ it.each([
 ])("shows %s recovery from the live socket", async (refusal, text) => {
   await refusedLive(refusal);
   expect(await screen.findByRole("alert")).toHaveTextContent(text);
-  expect(screen.queryByRole("button", { name: "Sign in" })).toBeNull();
+  expect(
+    screen.queryByRole("button", { name: "Sign in with builderlab.example" }),
+  ).toBeNull();
 });
 
 it.each(["adapter-refused", "grant-refused", "invalid-response"])(
@@ -87,7 +96,9 @@ it.each(["adapter-refused", "grant-refused", "invalid-response"])(
       "Restart Buzz to try again",
     );
     expect(screen.getByRole("button", { name: "Chats" })).toBeVisible();
-    expect(screen.queryByRole("button", { name: "Sign in" })).toBeNull();
+    expect(
+      screen.queryByRole("button", { name: "Sign in with builderlab.example" }),
+    ).toBeNull();
     expect(h.connects()).toBe(1);
   },
 );
diff --git a/src/features/communities/CommunityDialog.test.tsx b/src/features/communities/CommunityDialog.test.tsx
index abbc575532..649a9a5627 100644
--- a/src/features/communities/CommunityDialog.test.tsx
+++ b/src/features/communities/CommunityDialog.test.tsx
@@ -680,13 +680,22 @@ it("offers federated sign-in when joining refuses for it, then lets Continue run
     "wss://relay.example",
   );
   await user.click(screen.getByRole("button", { name: "Continue" }));
-  const signIn = await screen.findByRole("button", { name: "Sign in" });
+  expect(
+    await screen.findByText(
+      "This community requires builderlab.example sign-in.",
+    ),
+  ).toBeVisible();
+  const signIn = await screen.findByRole("button", {
+    name: "Sign in with builderlab.example",
+  });
   refuse = false;
   const requests = vi.mocked(fetch).mock.calls.length;
   await user.click(signIn);
   expect(h.service.signIn).toHaveBeenCalledOnce();
   await waitFor(() =>
-    expect(screen.queryByRole("button", { name: "Sign in" })).toBeNull(),
+    expect(
+      screen.queryByRole("button", { name: "Sign in with builderlab.example" }),
+    ).toBeNull(),
   );
   // Completing login replays nothing captured before it.
   expect(vi.mocked(fetch).mock.calls.length).toBe(requests);
@@ -748,7 +757,11 @@ it.each(["edit", "close"])(
     const field = screen.getByLabelText("Community URL");
     await user.type(field, "wss://old.example");
     await user.click(screen.getByRole("button", { name: "Continue" }));
-    await user.click(await screen.findByRole("button", { name: "Sign in" }));
+    await user.click(
+      await screen.findByRole("button", {
+        name: "Sign in with builderlab.example",
+      }),
+    );
     if (change === "close") view.unmount();
     else {
       await user.clear(field);
diff --git a/src/features/federated-identity/CommunitySignIn.test.tsx b/src/features/federated-identity/CommunitySignIn.test.tsx
index bf27211aa7..de3d423b44 100644
--- a/src/features/federated-identity/CommunitySignIn.test.tsx
+++ b/src/features/federated-identity/CommunitySignIn.test.tsx
@@ -27,22 +27,32 @@ it.each(["storage-unavailable", "storage-denied"])(
     expect(h.service.signIn).not.toHaveBeenCalled();
   },
 );
-it("requires explicit sign-in before retrying protected community admission", async () => {
-  const h = federatedFixture();
-  const retry = vi.fn();
-  render(
-    <CommunitySignIn
-      identity={h.service}
-      error="Federated sign-in is required"
-      retry={retry}
-    />,
-  );
-  expect(h.service.signIn).not.toHaveBeenCalled();
-  await userEvent
-    .setup()
-    .click(screen.getByRole("button", { name: "Sign in" }));
-  expect(retry).toHaveBeenCalledOnce();
-});
+it.each([null, "Builderlab"])(
+  "names server %s and requires explicit sign-in before retrying admission",
+  async (organization) => {
+    const h = federatedFixture();
+    const authority = h.service.snapshot().authority;
+    if (!authority) throw new Error("Fixture authority missing");
+    h.publish({ authority: { ...authority, organization } });
+    const server = organization ?? "builderlab.example";
+    const retry = vi.fn();
+    render(
+      <CommunitySignIn
+        identity={h.service}
+        error="Federated sign-in is required"
+        retry={retry}
+      />,
+    );
+    expect(
+      screen.getByText(`This community requires ${server} sign-in.`),
+    ).toBeVisible();
+    expect(h.service.signIn).not.toHaveBeenCalled();
+    await userEvent
+      .setup()
+      .click(screen.getByRole("button", { name: `Sign in with ${server}` }));
+    expect(retry).toHaveBeenCalledOnce();
+  },
+);
 it.each(["binding-mismatch", "authorization-denied"])(
   "explains %s without a session to switch",
   (failure) => {
diff --git a/src/features/federated-identity/CommunitySignIn.tsx b/src/features/federated-identity/CommunitySignIn.tsx
index 12274bb6ab..4474794351 100644
--- a/src/features/federated-identity/CommunitySignIn.tsx
+++ b/src/features/federated-identity/CommunitySignIn.tsx
@@ -129,8 +129,10 @@ function Action({
   )
     return null;
   if (state.status === "signed-in") return null;
+  const server = serverName(state.authority);
   return (
     <>
+      <p className="text-body-sm">This community requires {server} sign-in.</p>
       <Button
         onClick={() => {
           setFailure("");
@@ -147,7 +149,9 @@ function Action({
           );
         }}
       >
-        {state.status === "signing-in" ? "Cancel sign-in" : "Sign in"}
+        {state.status === "signing-in"
+          ? "Cancel sign-in"
+          : `Sign in with ${server}`}
       </Button>
       {(failure || state.failure) && (
         <p role="alert" className="text-body-sm text-danger">