GERN Industries Gibson Works...

[doctorwayne]

What would the marks look like in 1900?

I'm not sure, but they wouldn't likely have been on covered hoppers.
Back in those days, I don't think that the regulations would have been too stringent: probably the name of the car's owner, for instance, UNION PACIFIC, or the appropriate U.P. initials, and the car's number, but I don't think that any particular placement was proscribed. I couldn't find much in the way of on-line prototype photos, but most of the other data which we see nowadays could be placed almost anywhere on the car (if it appeared at all). Many cars also featured advertising, either for the owner road or for important on-line customers - this pre-dated the era of the so-called "billboard reefers", but was similar.

There's some info HERE on more recent lettering requirements for freight cars.

Wayne