Vehicle registration plates

In my country vehicle registration plates start with prefix depending on region of country.
We (polish community) would like to tag it under boundary=administrative of corresponding administrative area, but there is no established tagging for that yet.
In Taginfo I found vehicle_plate_code=* and license_plate_code=*. In our discussion vehicle_plate_indicator=* was also proposed, and I am thinking about sth like vehicle_plate_prefix=* (but I don’t know if it is prefix for other countries).

Do you have any suggestions for tagging? What would you recommend?

In my country first letter of registration plate corresponds to admin_level=4 and next 1 or 2 letters corresponds to admin_level=6


I would go for one of the tags in use (probably license_plate_code), and also document the use in the wiki

In the DACH countries it is also a prefix, but I don’t think that applies to all countries. In France, as far as I know, they simply count up at the front depending on the year of registration. Therefore license_plate_code seems suitable. Examples in my area here:

Swiss and Austrian states seem to use just ref?

What would be relevant, at least for Germany, is that there are also boundaries with more than one prefix. In the Bodenseekreis, you can choose from three prefixes since the last reform: FN, TT and ÜB. The last two are still the old licence plates which have now been made possible again.

In the U.S., where each state has a separate vehicle registration system, some states still prefix license plate numbers with county codes, but this practice is dying out, so I don’t recall anyone ever suggesting tagging for them. Even in the states that still allocate vehicle registrations by geography, the codes aren’t necessarily a good fit for administrative boundaries. For example, what if two counties share the same overflow code but otherwise use their own codes? What if the prefix indicates a state highway police district, but we don’t map the state highway police districts because they aren’t verifiable?

That said, many states indicate the county on the license plate using a sticker rather than incorporating it into the license plate number. Some states spell out the county name, while others assign an alphabetic or numeric code. Should these codes be tagged similarly to license plate number prefixes? Why not treat them as a kind of ref:*? Some states have parallel systems of county codes, one of which is used by the motor vehicle registrar, another by the highway department, another by the fire department, etc.