beautifull, BUT! can it be incorporated into SIGNATURE rather than self-standing layer?! There is signature image options for each usergrop in AdminCP->Usergroups->Usergeoup Manager->Edit Usergeoup (I have 3.6 adminCP so i look it from there), so why don't you move it in single block, called for example "Signatures" (same as Avatars or Smilies) and put all that pictures there with usergroup permitions and more? Basicly same stuff as Avatars, but for signature!
Hope you got my idea and I hope You will like it