I'm not a lawyer and this isn't legal advice, but that shit is not at all legal. If you want to assert dominance you are free to wait until this dbag is on duty and in the breakroom with as many people as possible, then very clearly discuss your wages while maintaining eye contact with Jer. If he's dumb enough to put up that sign, he might just be dumb enough to fire you/retaliate against you in front of witnesses. Employment lawyers literally salivate about slam dunk cases like that. If he's the owner his ass is grass and Uncle Sam's gonna mow it. If he's just an arrogant employee, his ass will be out of a job when your employer gets investigated. You, on the other hand, get a tidy sum of cash and a raging justice boner that just won't quit. Granted it could take months to shake out. So only do that if you can survive that long.