Based on the Sonceboz 246. Modifications to the balance and cock by Bulova.
Both have marks at the left upper edge of the detent screw, which is on the right of the crown when facing upright as in top pic.
Janet's example also has a larger circle to the right of the smaller ratchet wheel.
Janet's 1924 16 jewel w/ Asterisk date stamp.
stuartbaker104's 1926 15 jewel 6N w/ Triangle date stamp (from 1926 Princine watch record).
I'm having trouble seeing either the Asterisk or the Triangle in pics above, but we double-checked with both watch owners for conformation of date stamp.