We're using Google Apps for our domain with Gmail. We'd like to set the signatures for each user and rather they not change it. We're currently using Wisestamp for signatures and have a password on it to prevent them from changing it but since it's stored locally it's a pain to have to change it. Is there a way to control the Gmail signatures of our users through some centralized location?
Without looking to other marketplace apps you could try using the built in Append footer feature in the email settings for Google Apps.
Also it appears you can use the Google email API to update settings for all users gmail accounts. This might be useful. See this Gmail Signatures help article.
Since you're already using the product, we've recently launched a Corporate version that lets you do exactly that - centrally manage the email signatures of your domain, and whenever you wish to make a change it will auto update in your employees' signatures.
The site for the newer version is http://wisestamp.com/corporate
Disclosure: I am affiliated with WiseStamp