We call`em stickers.I guess it goes back to original licensing.You`d get a "tag" once registration was paid,just like a hunting license.The plate came along as a better way to permanently display registration.I think it`s funny how many people refer to their license as plural..."I lost my license.I need to get them back".That would be licenses if there were more than one.
I`ve never seen it done on these trucks.It would be a nice mod.I wonder if you could cut it out and use a rescess from a car rear bumper.