US Air Mail Question

So I think I have a AP15 not sure of it's colour type
Not that great at identifying the colour differences
And I'm also curious about the overprinted plane
Didn't find it in my books or web
Is it issued for private use or something like that?
perforated holes are CS then RCS

Scott C23 (design AP15) I would not get caught up in the natural slight shade differences of this issue. The odds of a rare shade are infinitesimally small.

The "overprint" is a slogan machine cancel used in several dozen US cities to promote airmail use. It was used on all mail, not just airmail. Here is a typical example:


The RSC is a "perfin" identifying the user and a way to deter employee theft. Perfin pattern R-128.5 in the vintage perfin catalog I have handy is not identified to a user.

RSC : Riley Stoker Corporation? or Republic Steel Corporation?

Thanks John
Appreciate the help

Thanks vayolene
Appreciate it