I thought the armband was resistance. I have seen a picture of resistance fighters on a BMW outfit wearing similar armbands. I will see if I can find it again.
At first glance I thought the armband was the DR blue and white, but looking at it closely, it does appear to have colored stripes top and bottom, white in the middle.
Not really an M23 because this is clearly a wet sump engine which dates it 1936 or earlier. Also it has a bolted up frame with a forged backbone. Hi twin port exhaust system leaves Blue Star or 1936 Empire Star as real options. Since it has a tin chain case as opposed to alloy it is a Blue Star. The picture doesn't who enough details to date it more exactly but it is continental bike because the tail light it on the left instead of the right. I think the armband is red white blue which is our national flag.
I couldn't find the picture I was looking for, but would agree that the armband is Red, White & Blue. I have seen many photos of resistance fighters (Dutch) wearing a similar armband, though this varied from area to area and political allegiance. This guy looks similar but with a different armband style.....