Biclycle plates
Holland has milions of biclycles and some of them have licenseplates. For example the bikes from Kronan. Kronan is a Swedish Bike manufacturer. Strong no nonsense bikes based on old models from the army of the 50s. Every Kronan bike has it's own licenseplate which is also the framenumber.
Link to Kronancykel Sweden. Other bikes with plates are usually rentalbikes.

Kronan bikes

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Car of the manager of Kronan Bikes in New Zealand

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Other bikes