I took my plate and plate holder off and simply put the screws back into the holes in the bumper..
my cars black and so are the screws so you can barely notice them...
You can also get bumper plugs (which i dont necessarily like only cuz they stick out too far).. i think you can order them the color of your car...
last thing ive seen are these vinyl round stickers (bout the size of a dime) that body shops usually have.. they would paint the color of the car and you stick them over the holes.. its still visible, yet less than a bumper plug cuz its flush..
2008 E92 M3 (03-08-2008-first delivery)
JET BLACK on BLACK w/Carbon Leather, 19's, Tech, 6spd..