A certain rifle scope from china looks very similar, (not identical aesthetically, and significantly different internally,) to one sold by a brand name rifle scope company. The cheap chinese varient comes with a disclaimer stating that they are in no way affiliated with the Brand name item. There is no logo on the chinese varient either. The purpose of the knock off is for a young adults game called airsoft. The brand name item is intended for firearms. Is it legal to sell the chinese knock off in the U.S.? Are knockoff's in general legal if they do not have any indication of affiliation with the brand name company? If it may be legal how can the item be named? For example if the brand name company has a model "551" can the knockoff company have a model "551.0"?