As a followup to my previous post about changing the e-mail signature on your iPhone, I wanted to point out that it’s also possible to configure Gmail (or Google Apps) to use different signatures when using the mobile vs. desktop interface.
To do this, simply navigate to the Settings panel from within Gmail Mobile (this is typically what loads when you visit Gmail from an iPhone or Android device). Once there, tick the box to “Use mobile instead of desktop signature”. You can also modify the text, which reads “Sent from Gmail Mobile” by default.
From that point forward, your messages will have the standard desktop signature when sent from the desktop and the mobile signature when sent from a smartphone or other mobile device.