Name of who made it.
your question is not specific enough, .30 cal carbine can be anything, as for 1944 can also mean a very wide range of firearms. for the two I know of: M1 Carbine, .30 carbine caliber, semiautomatic carbine Inland - around $800 Mosin Nagant M44 carbine, manuf 1944 in very good condition (like if you bought "new" from a store) around $90. there are hundreds of ".30 cal carbine" that are also manufactured in "1944".
postal
RC=Regular Carbine
A system of postal codes
Air mail.
It's "Codigo Postal" and it means Zip Code.
It depends on which country you mean. Many countries increase postal rates annually.
The meaning of codigos postales in English is postal code. Postal code is primarily used for postal purposes and locating locations where mail can be delivered among other things like packages.
MS is the postal code for Mississippi.
Regular Carbine.
Name of maker or sub contractor
postal code