Does anyone know how to add a signature to text messages with the Droid Eris?
I definitely suggest getting Handcent SMS in the marketplace. You can add a signature like you want and also a bunch of other stuff. You can also make it auto split texts as well, unlike the built in messaging app. It's free too, so its worth the download in my book.
Open Gmail > Menu > Settings and it is the first option at the top of the scrren.