These are English made Victor (over) 500 side cover panel varnish transfers for BSA B50 Trail 1971 B50T. I've added a photo of this decal on a 1971 Victor 500 Trail and also from a steel side panel cover I had sold. The 1972 B50T side panel decal is a different orientation and design, but they are also hard to find. Sold in pairs with instructions for applying varnish transfers.  

My name is Tony Schanz, I formerly ran DomiRacer Distributors in Cincinnati, Ohio buying and selling vintage English, Italian, & German motorcycle parts, tools, accessories & memorabilia. DomiRacer closed 6/11/2013, but I still deal in parts, motorbikes, decals, advertising, photos, posters, & more. Please add my store, The Real DomiRacer, to your favorite sellers and watch for other rarities in my future eBay listings.