When our Spyder was delivered, there were two velcro buttons stuck to the fender on the lower edge where the plate hits. You stick the opposite part to the license, and it secures the bottom. The parts book shows them as #293740028, but calls them dual lock washers, so I am not positive that is the right part. They also specify four, so they may be used at the top, too. Seems like I used rubber washers there, but I could be wrong. I imagine any 3/4" velco stick on buttons from a home improvement store would do just fine. Your Spyder probably didn't have them due to being repainted before you received it.
-Scotty