antique sterling tea set

There is a teapot,creamer,sugar that i found at flea market with all the same mark, when i got it it was almost totally black it took a lot of cleaning i still have work to do on the inside. I believe it to be very old but the mark i cannot find anything on, it seems to be made in two sections, the mark is a teapot and i can make out 3 letters on it they seem to be 5c2. could someone help me if they can. added a tray but not the same it is e-plated.