I like this idea

This actually seems quite a simple task to do..I support.

I'm not meaning to dampen the idea, but it's easier said than done.. Maybe you can search on Bukkit for a plugin that does that, but I doubt there would be a plugin allowing you to do that singularly. I'd expect it to be in a larger plugin as a hole, similar to essentials where it has multiple commands, and that wouldn't be healthy on the server if Fatnoob was to get a large plugin just to provide the sign editing. It's a great idea, don't get me wrong, but it might be hard to find something like that.