When were reporting marks, or car initials, formalized?
I know car initials were used in the early days, but when did MCB, or ARA, establish a national list of which railroad used which reporting mark?
I have a Google copy of the MCB 1911 Code of Rules, and it has listings of railroads and car owners, but no car initials.
A search of STFC archives reveals that the 'X' was first used after May 1910. This may also be the date that the four-character practice was established, although there were numerous examples of many more characters and '&' for many years afterward.
Horizontal 1-inch bars above and below started in 1918. AAR dropped the requirement in 1952, although many railroads started dropping them as early as the 1930s.
Periods within the car initials were dropped by many roads in the 1930s and 1940s. Like the horizontal bars, AAR apparently dropped the requirement for periods in 1952.
As for a date for when a nationwide list of car owners (railroads and private companies), and their recognized car initials, or reporting mark, I have a Google copy of a 1911 ORER, and I don't see any car initials being used. I also have the 1943 NMRA reprint, and the NMRA 1953 reprint. Both show established car initials.
I have Westerfield's 1919 ORER on CD, and it shows "Reporting Marks" for each company and railroad. So, the change (or standard, or recommended practice, was sometime between 1911 and 1919.
I was asked a question a week or so ago, about how a company goes about getting its own reporting mark, and how much does it cost. I got curious and created a web page with what I have found so far, for current usage. But I'm not have much luck finding a historical reference. But I suspect I'm simply looking in the wrong place.