I believe that the factory almost always stamped the serial number on factory installed sights. Sometimes where you cannot see them without removing the sights. They also stamped the sight blade on some models. Interesting gun and I have not seen a 38 DA target gun that was lettered as coming from the factory.

In the late 1800s and early 1900s, you could order target sights for additional cost and maybe the 1918 return was to have target sights added. They were available on Single Shots, 38 Single Actions, and Perfected revolvers, which are all the same top-latch as your top break. I think this one might benefit from a letter to determine originality, because I do not think many 38 DAs came with target sights.

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Gary
SWCA 2515