There are other methods like this, Sunshine Minting for example has a 'decoding lens' for their products that contain the 'MintMark SI security feature'.
Geiger Edelmetalle , on their Geiger branded stuff, uses a a UV safety coating but it will rub off with enough handling (which is why many of us do not remove the shrink wrap they put on their bars), they also individually assign serial numbers that can be tracked online for gold and silver bars starting at 1 gram