Exhaust actually is looked at during a safety. On a car, are the cat(s) present? Are there any holes/leaking joints in the exhaust that could cause CO poisoning to the driver/passengers? If the exhaust is aftermarket, is it properly installed? Touching brake lines etc? On a bike...is the bike equipped with passenger pegs? If so, could the slip-on burn the passenger? Is the slip-on mounted properly...away from brake lines/hoses/plastics? Does it exceed 90 DB? If so, this is where it's up to the mechanic (and his license) discretion. It is safety related 'cause you can't hear your surroundings i.e a car honking at you, an emergency vehicle (police, ambulance) behind you. Most aftermarket exhausts state "for racing only." Some mechanics will sign anything. Some won't. Typically a dealership will be more strict on safeties than garages as they have a reputation to uphold. I'd hate to be in the position of looking for my stock can that I threw away or donated out of stupidity. If the mechanic is a real prick, he can reject the silencer and ask for the OEM to be re-installed. He can do whatever he wants, it's his license, not the shops that's on the line with the MTO.
