Scratch

You can add a link, if that's what you're asking?
I've also seen someone with their project stats in their sig, but I couldn't say how to do that.
There's probably other different ways, too.

Well, here's the BBCode help page, http://scratch.mit.edu/forums/help.php#bbcode.
I'm pretty sure you can add a link to an image, so just look up your project's link, and shove it in there!

I think you're talking about updating what projects you have when they come out without having to edit the signature. Here's a forum post explaining how to do it.