allmost all states have 5 laws regarding plates. Maximum height from ground, minimum height from ground, maximum distance from tail lights height, illumination of the plate, and plate covers. In my state (FL) the plate must be illuminated by white light, must be at least 18 inches off the ground, must be positioed within 3 inches of the height of the tail lights. and may not be covered by any plate cover (including clear, smoked, or colored. I think it really depends on the type of law enforcement in your community. But make sure it is 100% visable and lit up by at least a white led light no matter where you put it. Also in FL its illeagel to place the plate on on the side of the bike attatched to the muffeler because it must be within 3 inches of the height of the tail light.
With great freedom, comes great responsibility.