http://www.bletchleypark.org/news/docview.rhtm/675670 says the red capsule attached to the pigeon is an Allied capsule, so if the code is German the message is from a German spy.
It's more likely the code is British. It has "AOAKN" twice - once at the start and once at the end, and from the digraph frequency (below), "AO" "FN" and "AK" stand out. I think that rules out any Enigma-based codes (e.g. the British
TypeX), as well as the US
SIGABA - the AOAKN would not be repeated at the beginning and end. I haven't found a description of BAMS yet.
Digraph frequency:
2 AR
2 DJ
2 GH
2 JR
2 ME
2 RZ
2 UA
2 OA, 2 AK, 2 KN (this is AOAKN twice)
3 AO
3 FN