Hmm... the whole 'deleting avatars and sigs' deal...
I can understand why they'd do that. If someone leaves a forum community because of something particularly serious, they might want to distance themselves from that group. Since they can't delete their own account, erasing the info from that account could be a symbolic way of demonstrating that they don't consider themselves a part of the group anymore. Kind of like moving out of a room, and taking all your pictures off the walls. If you don't feel that you belong in a particular place, why continue to have all the adornments and trappings that suggest you consider yourself a member?

Not saying I agree with it, I just understand where they're coming from.