I guess this covers it some but it does not mention what side
2B. Number Plates and numbers 1. ASMA requires all amateur racers to use a Yellow background with Black numbers. All experts are required to run White background with Black numbers. Front numbers must be at least 6 inches tall, while side numbers must be at least 5 inches tall. Numbers must be placed so they are easy to read from 100 feet away. If we can’t read your number you will not be scored
If it can't be read from the side of the bike facing the scorekeepers at start/finish, depending on the direction we're going...then you won't pass tech. If you need to put your number on the top of the tail because the tail is too small, we may require it to be on the side of the fairing. It's all up to the discretion of the head official and scorekeepers.
Had to have been in 2007, I'm fat in that picture (that's my ass hanging out in the background). Plus I haven't had to park on that side of the asphalt in years, dunno whose truck it is behind the Trail-90 (only one I can think of is Chandler, but don't think he visited in 2007).