TMK (Tax Map Key) is how properties are uniquely identified in Hawaii in the public records system, and it is really straightforward - the first digit is division/county, second digit is zone, third digit is section, fourth through sixth digit is plat, and seventh through ninth digit is parcel.

For example, in Hawaii the first digit would be the island ... 1 = Oahu 2 = Maui 3 = Hawaii 4 = Kauai
The second digit would be the zone - on Oahu ... 1,2,3 = Honolulu 4 = Koolaupoko 5 = Koolauloa 6 = Waialua 7 = Wahiawa 8 = Waianae 9 = Ewa
etc.

The way TMK works in Hawaii, you can tell an agent a TMK number and if they would pretty much know exactly where you were talking about without even going to a computer. I don't know of any other property ID number that you can say that about.

To adapt this idea to the whole US, we would need to pad this number out a bit to accommodate a bigger system - preceding the TMK-like number with a two digit state code, expanding the division/county into a two or even three digit number, and so forth.