Barrel markings on a Marlin Shotgun Barrel for choke

[BUSSMAN69]

I am trying to verify a Cylinder Bore choke restriction on a Model 26 Marlin pump shotgun. My experience with these old external hammer pump shotguns, is that if the barrel has a serial number. Then there is a letter after the barrel serial number, such as an "F", for a full choke. This model 26 shotgun has a barrel serial number, and after the serial number is a stamped symbol of some kind. Can't make it out though ?? Should this be a "C" for Cylinder Bore ?? Or did they mark the choke on these shotguns some other way possibly ? How can a person verify whether this is a Cylinder Bore on this shotgun from the factory ? Thanks ahead of time for any responses to this post.