I have never had any favorite number or such until I chose 41 as my number for running SCCA Autocross events seven years ago. I had 14 once but 41 fit better. So, for the Scooter Cannonball, even though it doesn't appear that numbers are required, or even wanted, I had my local graphic store make these for me. They are small, only 4" in diameter, but they will work fine.
They are magnets. Let's hope they stay on at 80+ mph.