@Ali-Hussain I'm doing something similar to this but with the borders. It would be easy to adapt this so that it sets the background instead.
It's essentially jQuery doing the legwork, but works perfectly.
I discovered that Admins (maybe mods tooP can see all signatures even if they are disabled for a group, i.e., nobody else can see them or set them. Is this intended behavior?
I ask because I migrated a bunch of signatures. I hate signatures but I want to offer them as a perk but I don't want to see everybody else's signatures that don't have the perk.
Maybe a permission to activate the setting?