Motorcycle Serial Numbers & VIN Numbers

Aermacchi VIN numbers

AMC AJS/Matchless from c1935
Engine numbers usually start with the year of production, followed by model designation, and completed with the production number of the motorcycle.
(Source - Wikipedia)

BMW Engine & Frame Numbers
Post-1969 BMW 650 numbers

BSA Serial Numbers 
BSA Numbering System
http://www.bsaoc.demon.co.uk/1931-40.html
http://www.bsaoc.demon.co.uk/post1960.html
BSA Frame Numbers at NSW BSA Club
http://www.bsansw.org.au/scgi-bin/bsadate.cgi
BSA Numbers at moto-anglaises.com
http://www.motos-anglaises.com/technique/index.htm

Lambretta
http://www.scooterhelp.com/serial/serial.numbers.html

Maico
Maico Numbers at Maico Madness
Maico Numbers at off-road.com

Montesa
Montesa Numbers
Montesa Capra Numbers

Norton
Norton numbers at moto-anglaises.com
Basically the same information here:
http://www.britishspares.com/42.php
http://www.bmh.com.au/norton/modelnum.php

Penton
Penton Identification - KTM, Sachs & Puch engine information
http://www.pentonmotorcycles.com/page3.html

Triumph
Triumph Serial Numbers at Bikelinks
Triumph engine & frame numbers
T120 & T140 Engine Numbers
Triumph Twins
http://www.motos-anglaises.com/triumph/numero.htm

Velocettte
Velocette LE Engine & Frame Numbers
KTT engine numbers

Vespa Identification
http://www.garnersclassicscooters.com/Vespa-ID.htm
http://www.scooterhelp.com/serial/serial.numbers.html

Villiers Engine Numbers