Amongst proof marks are codes enabling one to determine the date of manufacture of many guns.
Birmingham, England: date code letter placement:
1921 - 1941: Letter at top of intersection of crossed swords. Number of dots beneath to indicate inspector.
1950 - 1974: Letter at left of intersection of crossed swords. B at right. Inspector's number underneath.
1975 - 1984: Letter inside upper left of circle. B at upper right. Inspector's number at bottom.
1985 - 1997: Letter at left of intersection of crossed swords. C at right. Inspector's number at bottom.
London, England: LP over 2-digit year; began relatively recently.
Gardone, Italy: Month and Year in Roman numerals until 1945. Unornamented Roman numerals from 1945 until 1975, then a two-letter code surrounded by a small rectangle as per the chart below.
Eibar, Spain: When an N has a "~" over it, it refers to the second of its respective year.
Suhl, Germany: Month and year, 3 or 4 numerals as required, with forward slash between month and year until 1930s, as: 5/24 for May 1924. Afterwards without slash, as: 1163 for November 1963.
Ferlach, Austria: The proof house's number, followed by a dot, then by a 2-digit number for the year, as: 346.33 for the 346th gun proofed in 1933. During the 1980s a three letter code was adopted, for example: ETR, where the first letter is the month code, the second letter is always a T and the third letter is the year code---see chart below.
Ferlach Maker codes, post 1945 - xxxx being the maker's serial number
21.xxxx Josef Fanzoj
22.xxxx Josef Hambrusch
23.xxxx Karl Hauptmann
24.xxxx Josef Just
33.xxxx Franz Sodia
35.xxxx J. Outschar
37.xxxx Benedikt Winkler
40.xxxx Ludwig Borovnik
42.xxxx Josef Winkler
Other Date Codes: