Classic Motorcycle Numbers Motorcycle Serial Numbers & VIN Numbers Motorcycle Serial Number Locations These vary considerably from marque to marque Engine Numbers Check these locations: Below the barrel stamped into the crankcase. On the front of the engine stamped either side of the crankcase join.
Below the clutch / transmission area. Rear of cases below carburettor area. Frame Numbers. By far the most common location is on the steering head. It may also be found on one of the rear downtubes or on the front downtubes. 
Other locations include: top tube below fuel tank; lower frame rails; swing-arm pivot area. Motobecane Mobylette 1968: Forward of the rear wheel axle on left side.
For production number and year manufactured information, click on the 'Year' link in the tables. Serial Numbers (1. Ferguson ariva 150 combo firmware patch. 3 on a letter code, production number and ending letter(s) and number code were used in the serial number to denote the model, production number and month and year of manufacture.
Matchless pre-1958: Directly below saddle on upper frame rail joint. 1958-59: rear of front downtube. 1960-67: right downtube below headstock. James Rigid frames: usually stamped on the lug beneath the saddle on LHS Plunger frames: saddle lug (same as rigid), or on the steering head, LHS Swing arm frames: stamped into steering head and/or into a steel ID plate pop-rivetted onto the steering head. AJS and Matchless • AJS/Matchless from c1935 AMC engine numbers usually start with the year of production, followed by model designation, and completed with the production number of the motorcycle. (Source - Wikipedia) Jampot has sections on serial numbers.