Well, if you can, then I suggest to limit the (displayed ?) lines, because you are right that URL's can take quite some space.
Take my sig for instance. It's fine to me and I think the length is acceptable, but I wouldn't cry If I had to remove one line. Posting some sort of advertising of your project is the best usage of the sig. The other stuff is not really necessary.
On the other hand, I do not know how it turns out technically. Are huge sigs bad for the page buildup time ? Also I think I've seen another forum, where you can simply turn a switch in your user profile and no ones sig is displayed for you.
To be honest, I really don't care about people sigs. If they are too long, it disturbs your reading flow (because I wanna read posts, not sigs), the only thing that I disliked is the scrolling problem, that was a bad solution IMO (and honestly, no one will have scrolled down the sigs on purpose just to read it, right ?
). Of course it's nearly impossible to make everyone happy, but it's an admins call in that
