update: As of November 2008, gmail now has a setting to place your signature above the quotation if you want to. Thanks Google!
When you reply to a message, Gmail creates a text editor with your cursor at the top, a giant quotation containing the message you're replying to, some useless double-colon separator, and your signature.
Gmail's default cursor location encourages top-posting, which I don't really mind. The problem is that the signature is bottom-bosted, so people tend to write a second signature above the giant quotation. A few wasted characters, not a big deal.
The real problem is that I know that Gmail has stuffed my signature down there at the very bottom, so I'm moving it back up every single time I reply to an email. Were I in Vim, this would be just another few wasted characters ("GD``p"), but I'm not and I grew annoyed. So I automated it.
Here it is: uppersig. It's a bookmarklet, so don't bother clicking on it now, it won't lead you anywhere. But if you put in in your toolbar, and click it immediately after hitting "reply", it will move the signature and refocus the editor.
edit: by the way, Google often changes internal Gmail details which break my script, but I fix it everytime, so just bookmark a fresh copy if you ever find that my bookmarklet stopped working. Last updated 2008-09-19.