What google image can I use on my site for "Sign in to Google"

I am creating a web application and I need it to have facebook and google authentication, but I cannot find any information on using google policies to use brand image for this case.

For facebook, I found this:

https://www.facebook.com/brandpermissions/logos.php

but i can't find a similar page for google brand image, all i found is this:

http://www.google.com/+/business/brand-guidelines.html

but they don't talk about login.

Thank you very much for your help.