Regardless of the code system you adopt, you should assign individual asset numbers and permanently affix them to each asset. You can attach the identification number to the asset through labels, tags, decals, epoxy paint or other appropriate method. Attach the number in a conspicuous place where it will not be worn or knocked off. Try to standardize the location.
It may not be practical to place a number on some items. In these cases, assign numbers, and indicate on the cards that the number is not present.