Serial numbers for Rolf Prima wheels are located under the rim strip, near the valve hole on many models.
Note: TdF (carbon tubular rims), Alloy tubular Cyclocross models and Ralos and Rage models have their serial number on the rim near the "American Flag" decal.
Steps to Locating the serial number:
1. Remove the tire and tube
2. Remove wheel rim strip
Use a flat-head screw driver to pull the rim strip up and away from the valve hole while placing the rim strip off to one side of the rim. That way the rim strip can be reused.
If you can't find the serial number, check that it is not affixed to the backside of the rim stripe.