The cap is not made by Leitz, but by C&P themselves. Maybe during the war. No copyright problems in those years. Did you ever see a rubber lens cap by Leitz? Or a 40mm cap? I should have know it after 40 years of Leica´sm. And I found the cap on eBay in England.
Leitz never wrote "Leica" on lens caps that were not for a Leica, such as caps for lenses for projectors, enlargers or binoculars, always only "Leitz".