FTFY. it's one of those things that isn't usually enforced, but if you've (the general "You") done something to catch the officer's eye that they want you to stop and have a chat, you've pretty much it pretty much handed them a reason.
reason given for my last traffic stop? trailer ball on the bumper obstructing the plate. further back, i've also been stopped for no light on the back plate, which led into Mr. CHP (literally) bringing out the code book to look for things to check, including bringing out the tape measure to check the height of my headlights. in the end all he found to write was that missing license plate light and a lack of a front plate, but missed the limo dark (5%) front windows, and how low the rear plate was mounted (under the bumper on that car).