I'm not 100% sure but I don't think you need one, look at something like a Harley-they don't have any kind of spark arrestor. But as soon as you "modify" your exhaust it will get louder which technically makes it illegal and you could get a ticket. I'm sure you could take it out and get away with it but there is always the possibility for getting a ticket.
It would be "louder" but it still wouldn't be too loud. That's if you're talking about removing the sparky from the stock exhaust. Most, if not all, aftermarket pipes have removable spark arrestors. Depending on the pipe, that can get pretty loud. But you'll most likely still be okay.