I'm going to suggest limiting images in sigs to no more than 120 wide by 60 high, and to restrict the text to 5 lines at the most. I could go into long and somewhat convoluted rationale's for it, but, basically, its a workable methodology that allows for people to have a pleasant image and or a complex signature without interfering with the informatin presented in a negative manner. OTher than that, the only restrictions I'm going to suggest are that the same ones that apply to adult site linking apply to siglines (no links to adult websites). well, all except maybe Raunchyminds...

thou and I, my friend, can, in the most flunkey world, make, each of us, one non-flunkey, one hero, if we like: that will be two heroes to begin with. (Carlyle)