The trademarks are different for sure, but the styling is different for appearance. The first thing you see when you get the lens is the lens cap. Also, Canon's low-end lenses have side-mounted lens caps. Sigma's lens caps are basically medium-sized, which is convenient for wearing with a lens hood. If the size is different, it has nothing to do with the brand, it's just a different caliber. Canon also offers small and large sizes.