Hi,
I can't help you with the 50s, but....
I remember Rivetts in the East -End of London, they were mainly selling leathers & accessories in the 80s, if I remember rightly the shop was on the left-side of the road, which was Leytonstone High Road leading to Leytonstone Road, heading south towards Stratford.
I just found an address in an old magazine Motor Cycle Mechanics June 1972 234-8 High Road Leytonstone E11; 01 504 1304, obviously this is the old London code @ this stage they were importers of Moto Guzzi machines.
http://www.visordown.com/features/groovy-motorcycle-ads-from-the-past/19591-13.html Here's a link to past Rivett's adverts, a logo or symbol could be copied from here perhaps!
Are they still trading?
Check it out!
Hope this helps
Cheers
JBW