Gentlemen,
Looking for some more information about the above photo I came through another one (this time even in color!), showing the same style of alphanumeric code:

Above is the photo as I saw it for the first time in the www. The code on the wing is almost non visible. With some photoshoping (I didn't go too much in restoring the photo, but just making it a little bit clearer) the code A8 came to the light:

The fuselage number is A8 too, but there is also another one, probably written with chalk and it seems to me it's S2 or S3:

The national insignia is overpainted in the same fashion as on the first 2 a/cs. It's easy to think this might be an "Avenger" from the same unit.
Since the plane is shown on a carrier deck, could this be an operational a/c rather than a training one? Or maybe from an OTU?
AFAIR the 2 freshwater carriers "Sable" and "Wolverine" in Lake Michigan had some TBF's. There is a
very good thread in this forum with many photos, but all the "Avengers" are coded with
T (I guess for torpedo bomber) and the "Dauntless" e.g. are coded with
B...
Or could the alphanumeric codes A* and S* be local markings from the Pacific?
Like with the "Avenger" below (obviously from a later period), coded S83 and named "Queen of Rabaul":

Cheers!