that's an old K Constantinople made in Turkey earlier than 1940 on back
https://robscott.net/cymbals/k-constantinople/
have to click on page pictures if don't show up they're there just not there they open in another window (lol
no one- altho they make excellent bottom hi hat cymbals- care too much about old K Constantinoples- they were primitive compared to the old K Istanbul that were to follow. There are a few old K Constantinoples on Ebay at the moment no reserve and a Lot of bids
I would keep that as a 15" hi hat bottom as it will never let you down