Deep in the family box

I found these soldier stamps. Issued by a carrier pigeon unit as part of the mobilisation in 1939. 

At the beginning of the Second World War in September 1939, the units began issuing attractively designed soldier stamps. The net proceeds went into the units' welfare funds, which were used to support needy soldiers and their families. However, they had no franking value, as military mail was carried free of charge, as it is today.