I'd say its a square and along with the case serial number starting with a 6 would agree with the 1936 date. Other 5ABs I have seen are 1936 & 1940.
Ahh, I just noticed the "BULOVA' on the crown. I'm not sure of they did this in the 30s (could be a replacement crown though) Anyway have knowledge or experience with signed crowns and when they started being used?
At this stage this watch is 'Unknown'.
We have several examples of 5AB in the watch records through 1946. I updated the mvnt database to reflect this. Dr Ranfft gives a start date of 1936 without an end date. His example picture is that of a 5AC dated 1949, but I used the known date from our youngest example (1946). Don't know about the signed crown start date.
I found this picture of a different 5AB from 1936 on another site.
Although THIS IS NOT MY WATCH, does the fact that the position and orientation of the square (on the clearer picture) matches my watch make any difference?
Shame we can't see the crown on this one!
There's another 5AB movement from 1946 on this site, which doesn't have a signed crown
http://www.mybulova.com/watches/1946-margo-4538
But a quick google found this (link below) on ebay, with a circle date stamp (1934? 1944?), which does have a signed crown:
http://www.ebay.co.uk/itm/4U2FIX-Bulova-5AB-Caliber-17-Jewel-Movement-R…
I guess replacement crowns are commonplace though...
1946 is my guess, as this is so similar to many of the styles of this year.
This Duchess ad from 1946 is almost exactly the same, but I can't tell if the diamond section has the same amount of stones or if it is flat or curved like the subject, but it shares the same strap mounts,,which are very unusual.
Also similar to the Carol in this 1946 ad.
http://www.mybulova.com/sites/default/files/vintage_ads/1946_AD6.jpg
Or even a "Her Excellency" variant, subject has a lot in common with these models in this 1947 ad.
http://www.mybulova.com/sites/default/files/vintage_ads/bulova-ad-1947-4.jpg