Signature Length

[PrizeLive.com]

I'd search on the forum but I can't, "Due to high stress on the server, the search function has been automatically and temporarily disabled. Please try again in a short while."

Anyway, how can I limit a signature size based on a type of a member on my forum? For example, I'll have a group called, "upgraded members." For these members the signature length will be 300 characters while everyone else will just be 100 characters.

What's the easiest way to do this?