front bumper plastic blocking

[wvbball27]

ivee been noticing alot of the bikes with some type of plastic like a plastic bag or soomethign taped over there front bumpers. i was wondering if someone could help shine some light on what exactly that is? i had piece of carboard cut out then dicttaped and it looked ok but wouldnt mind knowing what everyibe else is using.
thanks in advance and a merry xmas to you guys!