As of the 5/21/2012, there is no need to implement a signature limitation for certain user(s). We (Uzi Gaming) strive to give members' freedom without limitation (with-in reason), therefore unless member(s) start heavily-abusing their signature permission, it would be pointless imposing a signature restriction.
Although; member(s) with rather 'large' signature image(s) are dealt with, such as removal of the opposing image, if that member continues to abuse their signature permission, it will be removed, simple.
:blackhat: