This lends some credibility to the widow story then. If a postwar flag had Kanji dedicated to the leader of this unit, and signed by the soldiers in it, that seems to be a scenario that could help validate the claim. It's a very symbolic sounding gesture, and isn't just some random flag signed by veterans. It was done this way with a purpose in mind. If it can be determined these men were all in that unit, and if the gentleman in the Kanji comes up as an officer or leader in that unit, it stands to reason either the story is true, or this guy bought a flag and had everyone sign it.
In any case, this is the sort of scavenger hunt that makes this hobby fun.