I also tried out here everything to find a code on the plane.. no chance...
There is a writing on the backside, but this is heavy "overpainted".. I tried to make carefully the writing visible, but all you can read (with really good will) is "gelbe" So maybe the stand something like "gelbe J". I don´t want to destroy the picture by doing more on it....
What me confuse is that no Werknr is painted on the tai on the second picture... Maybe in two weeks i will receive the field post letters i wrote about. With luck i can then "discover" the unit...