Its always good when an old thread comes back to the top, I will try to find my missing photos and repost, and I think there have been some more discovered since 2015.
In answer to your question they are often on the removable section of rear number plate just above the rear lamp, but in some cases on top of the rear number plate, on the side the tool box (one early BSA contract)or front of the tool box (some Matchless's) wrapped around a rear tube (RE) on the lower frame plate (later Welbikes).
