The case style is more early-mid 1930s and I believe we have seen Bulova watches in Star cases before (I think) Case serial number starts with a '2', so if it is an original watch I'd date it at 1932. However if the movement does in deed have a cresent moon date stamp I would agree with Geoff and say ita a Non-Conforming Bulova with a marrige of a Bulova movement and non-Buova case.
In reply to Is a case back hallmarked by William Smith
Let me rephrase above statement. I'm not finding any 6AF movements in our watch record database which also have movement serial numbers after 1932. There are examples in both the movement database and the watch record database later than 1932, however none of those movements post 1932 have serial numbers.
I believe the movement in this watch is from 1931 (square shield) and therefore based on the case SN, the complete watch is from 1932.
The earlier crescent moon date symbol may have been stamped when the movement SN was stamped, so if there's any patterns in movement serial numbers by year for 6AF, we may expect to see the mvnt SN corelation w/ the earlier date stamp (1928) rather than the latter 1931 Square Shield.