Depending on exactly what they look like to an experienced examiner, and where on the gun they're located, the marks could be assembly numbers or a date code.
You should find a date code stamped on every double-barrel shotgun in the Stevens brands, produced between March 1949 and December 1968.
Usually, it is behind the hinge pin or ahead of the trigger guard on the bottom of the frame.
It will appear as a small circle containing a number and a letter.
The letters correspond to the years shown in the following table.
A 1949 B 1950 C 1951 D 1952 E 1953 F 1954
G 1955 H 1956 I 1957 J 1958 K 1959 L 1960
M 1961 N 1962 P 1963 R 1964 S 1965 T 1966
U 1967 V 1968 W 1969 X1970
Without actually seeing pics, or examining your shotgun, I would make a WAG that it's from 1950.
