They already exist. You can also use free android phone apps and a ping test where the microphone can spot fake coins by resonance of the ping. Hell, I can tell the difference between real or fake with my ear with ease.
There are also things like the specific gravity test. It actually seems far easier to spot fake silver than fake gold because tungsten is EXTREMELY close to gold in the specific gravity test, while nothing to my knowledge is for silver, plus silver has several other unique traits gold doesn't.
They are not debt based instruments because they require no rent or energy input greater >0 to exist at all while bitcoin is a debt based instrument.