For instance, German license plate KA-WT 342 is from the City of Karlsruhe ("KA"), and is privately registered (letters after the dash).
KA-T 34H is a Karlsruhe privately-owned historic car (H at the end).
KA-4734 is a car owned by the Regierungsbezirk Karlsruhe (most likely a police car)
0 57-274 is a car owned by the embassy of Indonesia in Germany (0 for diplomatic, 57 for Indonesia)
BN-173-345H is a historic car owned by an UNHCR (173) employee with diplomatic immunity working from Bonn (BN). Cars owned by the UNHCR itself would be 0 173-788H...
This kind of quick-glance information gets lost when you introduce vanity plates.
We do have "Wunschkennzeichen", though, allowing you to choose the random letters and numbers from the pool of those combinations not yet used.