This has been talked about before, but for many reasons this has not been possible. ESPECIALLY if it were to be based on rep, would throw the system outta whack. Why? Because in reality reputation is not more than a bunch of numbers added together. Thats all it is. That's how SM faltered, it was based on rep.
So if everyone got a sif based on rep, people would work hard to get a proze they don't deserve.
Though I am no admin, nor a high ranking member here at TheHelper, so I can only say what I think. Sigs should be kept as they are, IMO, and for no reason really should that change, again, IMO.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.