Data on freight cars usually includes the dimensions of the car: this is usually located to the right of the door. Cars were required to be weighed every so often, this varied depending on the era and, I think, the car type. A car that had not yet been reweighed would have "NEW", followed by a date, such as 11-06-45. Cars that have been reweighed would have a station or shop symbol, usually two or three letters representing a particular location, followed by the date. You might also see "Return when empty to" usually followed by the name of the owning railroad and a specific location. Other notations referred to permissible types of lading, such as "Clean Lading Only", or "Hide Service Only". Some cars also bore lettering denoting special features of that particular car, like "Permanent Floor Racks" or "Auto Loaders". You can check in your local hobby shop for other examples: just open a few boxes and have a peek. Many manufacturers nowadays are making an effort to be more prototypical with their paint jobs and lettering. Another excellent resource, in my opinion, is the ongoing feature in RMC called "Essential Freight Cars", by Ted Culotta. Most of the cars dealt with are from the 1930s to 1950s. The modelling and photography are excellent, and there's lots of prototype information.
Wayne
