Currently on ebay is a photo of an Albatros B.II with B2 on the Rudder. The style of marking is rather unusual.
https://www.ebay.de/itm/226152399071...Bk9SR7q67qLyYw
A registration for the Prinz Heinrich Flug perhaps?
http://www.frontflieger.de/3prinzheinrichflug.html
Regards,
Clint