Russia C1 Identification

I think I found a Russia Airpost C1 in Grandma's collection. Unfortunately,
my Scott's album warns me, "No. C1 was on sale at the Moscow General
Post Office. Counterfeits exist." Any opinions on this one? Thanks.

Hi Partime,

I'm pretty sure this is a forged overprint as the tail should be more symmetrical.

I suspect that the basic stamp is forged also as I believe the P of POCHTA should have a flat top.

Hello partime,

below is an illustration from Lyapin's catalogue showing the differences between genuine overprint and 2 of the forgeries:



The first forgery in this drawing is characterized by the off-centered tail of the plane and by exaggerated curves to the wingtips.

The second forgery is characterized by a curved joint at the intersection of the body and the wing of the plane at left, rather than a more or less straight joint in the genuine stamp.

Below is my used copy of the stamp, which I think is genuine:



I would tend to agree with nigel's opinion about your overprint - forgery type 1 above.