I would have no problems with any member sending a polite PM explaining the sig limits to members who do are creating sigs for other people that are over the limits. So long as they're polite about it - remember, you're wanting to help them learn, not tell them off. Telling people off is our job.
As for people changing sigs really fast, I can't really see us being able to do anything about that, however if they are doing it on a regular basis than yeah, the best you can do is either let them know that it's rude to do so given the amount of time spent on such things or else just let all the sig-making types know about the person's antics.
