Guys, thanks for the suggestions.
It appears to be the case that the Germans assigned sequential numbers at each POW camp. Thus the number "3496" was used at Stalag Luft IV, but also at other POW camps, both those run by the Luftwaffe and at others. I am not sure if at Stalag Luft IV they assigned numbers based on the compound (camp), i.e. could there be a POW in compound A with number 3496 and another in compound B with the same number, etc. I would doubt that is the case. Anyone know for sure?
The US POW lists here:
https://aad.archives.gov/aad/series-...at=WR26&bc=,sl
did try try to record the camp a man was held in, even if in multiple camps, but did they not record the POW number. Using some "advanced search" methods, these records can be searched by month or day of capture and/or by state of residence so they can be of some use.
I have found that in some cases, POW numbers were recorded on the "immigration" records at New York harbor when the returning RAMP (Recovered Allied Military Personnel) ship docked. These records can be found on Ancestry but seem to be "searchable" by name only. It is possible to read through the entire records of a particular ship (some of these are hundreds of pages long).
I am reasonably sure the man I seek was an American Airman, most likely from the state of Wisconsin (possible Northern Wisconsin where the plaque was found, or an adjacent state, i.e. Michigan or Minnesota).