This SO: http://stackoverflow.com/questions/14177469/signing-out-appengine-app-without-signing-out-from-google-com/14178401#14178401

References this blog: http://ptspts.blogspot.ca/2011/12/how-to-log-out-from-appengine-app-only.html

Bug report with responses from official Google employees: https://code.google.com/p/googleappengine/issues/detail?id=5602

That last link is pretty outdated. It seems that deleting the cookies works just fine. Allows logging out of the app without affecting your Google login globally. Before, it would log you out of ALL of your accounts, including ones that you never signed into TBA with.