When a Google App file (docs, sheets, etc) is shared during a session:
a) If your Google account is not logged in to the current browser, you will see the message "initiate session" on the top right corner
Only if the presenter opens the document for editing, you will have the option to log into your google account
b) If your Google account is already logged in to the browser, your avatar will appear on the top right corner
(your name and email address will show when you hover on it)