I have all the usuall culprits on my 1924 or before gun but also a P with an asterix over it and an N with an asterix over it.

My gun looks to be exactly 1924 as it has the diamond with the 12 and the c in it. Has the lion over PV for smokeless and all the other markings. But the n and the p I don't understand. They are in line from top to bottom and are not combined with anything else. Also could someone tell me what choke 18.0 and 17.3 would translate into for this 12GA?