Signatures use the annoying British date format, 24TIME DAY# MONTHNAME, YEAR. I prefer the International format, YYYY-MM-DD HH:MM. I've found some code to add to my monobook.js ("Signature Fix.") which adds the signature I want when I hit the signature button on the edit page. I'd prefer ~~~~ to do this, but I don't see a way. The code has breaks in it to prevent wiki from parsing it, so for reference, the code looks like this:
It's kinda messy, but it comes out fairly short. Ideally, I'd like it to use Bitstream Vera Sans and Mono by default, but I think the extra HTML would be a little inconsiderate to editors. It looks like this:
For the record, I goofed up and included {{non-subst}} templates in my raw signature trying this out, and signed a few talk pages with it. One of them is permanently protected, so that's bad. I ran around fixing all the rest.