UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.84 Safari/537.36

Steps to reproduce the problem:
1. Open Google.com in the incognito window.
2. Click on sign in button on te top-right . 
3. Fill valid details .Then after authentication you will be redirected to home page . Now you will see the issue with sign in button. Signin button still say sign in. 
4.Again click on sign in button .I think now it checking for cookies and do nothing.But on home page of Google(technology leading company). It looks very bad that sign in button says to sign in even if you are already singin .

What is the expected behavior?
When you click on sign in button after authentication it need not to show sign in button again and again. 

What went wrong?
Sign in button on Google home page must be hide after a user successfully logged in.

But it does not happen.

Did this work before? N/A 

Chrome version: 51.0.2704.84  Channel: n/a
OS Version: Ubuntu 16
Flash Version: Shockwave Flash 24.0 r0

On a Google home page (A tech leading company).It looks very bad that sign in button says to sign in even if you are already sign In.