Maybe a rule on signatures isn't a bad idea....

To some people, having a lot of tickers is just annoying and ridiculous (I'm in that category), but others have a very valid reason for not liking them, such as dial-up issues and even joint discomfort from having to scroll down so much.

In the past, everyone has been more than willing to comply with the siggy cut-down requests, as well as other requests, such as not using all caps and not using netspeak. But if people are going to outright refuse several polite requests, a rule is probably the only option. You can't force someone to be courteous, but you can enforce a rule.