I will consider it.We are getting a dozen spam account from the same sources every day. Giving them a way to put a link in the profile accomplishes their goal and encourages them to do even more of it.
It's not just you. I am a long time donor. Can't edit my profile.I only became a forum donor a couple of months ago myself and was wondering the same thing.
I just changed the permission for Forum Donors to be able to add link to signature. Please try again. I also provided some other permissions.
Ah, found the problem. Forum donors should have full permissions now. Please try and report back.