Antique License Plate Bicycle, Sidecar, Motorcycle, Boat Mystery Maine

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Here"s one fresh from a barn in Maine. Unusual size 4 long by 2 1/2 high. It is red with silver paint. Not sure what it went on. Bicycle? Sidecar? Motorcycle? 
Has no state or date. Very interesting piece. If anyone has any ideas please let me know. Thanks for looking. 

Sale Price: US $20.00

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