Zur Einengung ist Kfz-Kennzeichen geeignet, was bereits in Leo ist als
licenceBE plate number [autom.] das Kfz-Kennzeichen
licenseAE plate number [autom.] das Kfz-Kennzeichen

A.) The plainest meaning of _Kennzeichen_ in text is exactly as I'm suggesting here. In my experience, it is very often used without a prefixed "Kfz-".

I'm thinking about the real-world user who sees this term in text and simply wants to know the everyday meaning of the word.

B.) Werner, if you think Wikipedia's got credibility problems, why immitate their mistakes by asking for references to, ahem, "reputable" web sites to "substantiate new proposals".

_We_ are your usage panel. LEO solicits input from the users. By and large, we're not stupid. Quite the opposite, most of us are keenly interested in language and make contributions drawn from our own experience that are obviously appropriate.

ON VEHICLE
6 [usually pl.] the pieces of metal or plastic at the front and back of a vehicle with numbers and letters on it—see also L-plate, license plate, number plate

(aus: Oxford Advacded Learner's Dictionary)

Außerdem lernt man es auch so in der Schule...