Where to find race numbers?

[Mapoipoi]

Newbie question here...
I often see the race guys with the yellow background and black numbers on their bikes.
Some of the trackday organizations this summer require a number on the bike, regardless of one races or not...
Where I can find these materials? or do the guys just paint them on the bike? I never got a chance to take a close look...

Thank you in advance for the help!

[1000RR]

If you just want a number for track days (no background color)... You could go the really inexpensive way and just take electrical tape that morning and do your own. Of if you want something more permanent, you can go to your local decal shop and have some made, or you could stop at your local CycleGear, they have em... or go online. I do the latter and usually get some made at speedy signs... you can customize it however you want by going to Lettering Tool at SpeedySigns.com

[npinto]

I buy mine from ebay. Just search " motorcycle number decals " usually pay about $10 bucks for three

[Slim]

go to your local decal supplier and ask for die cut numbers. likely will run you about 10 bucks