Most are useless on a vehicle that is easy to access. All they do is slow them down...which is a benefit. My cat pipe has been sawed through 4 times over the years. They get caught in the act and don’t get the cat. Etching is useless. Grind it off. Spray paint also useless . You can try an alarm system..but it might hack them off to do more damage
All these various tactics can’t stop a professional determined thief. They might stop a junkie trying to get money for a fix
Get one made of stainless steel. Thieves don’t like to linger, and stainless is much more difficult to cut than mild steel or aluminum.