You can buy the stick on letters and numbers for your boat, and they'll do the job. But, if you are fuss over every detail, check out having your registration number done by a graphics sign shop. I had mine done by a local fellow I've known for years. Cost forty bucks which included the application. He would have slanted the numbers to match the NITRO, but the state specifies "block" numbers and letters. Not being sure if it could be a problem, I opted out of slanting them.
While it may cost a few bucks more, they are more durable than the peel and stick type, and they go on as one piece with the top film peeled off once they are applied.