Gmail's support for just one email signature can be a pain if you don't always want to end your messages the same way -- you may not want to respond to a work request the same way you do an invitation to dinner. You won't have to fret about it much longer, though. Google is introducing support for multiple signatures on the web, with the option to make one of them the default. You just have to go into Settings > Settings > General to create a new signature, and a button in the compose window will let you choose and manage signatures while you're writing.