I believe it is USPC.

I also believe that it is dated 1939-1948. Post 1938 is the "dark period" for USPC. Records are available up to 1938. I believe that most uspc chips that are not in in the records are from the post 1938 period. Conversely I also believe that most if not all USPC chips made prior to 1939 are in the records.

Did I use the word "believe" a record number of times?