Although I claim no direct knowledge, the words 'inedible' and occasionally 'edible' were often found on tank cars originating from meatpacking plants. Yes, tallow was one, and some cars were actually marked 'inedible tallow'. There are probably some today.
I believe 'edible' was material that came off the packinghouse floor under the same conditions as the meat, that is, it was not contaminated in such a way as to render it unsafe for human consumption. More commonly, this same material was handled in ways that rendered it unfit for human consumption as part of its processing, before it was pumped into the tank car. This latter, of course, was cheaper, and was of no consequence if it was destined for a soap maker or other industrial use.
Examples of this processing might include being shoveled into a bin, or being hosed down from the literal floor, or stored in outdoor tankage, or being conveyed in industrial hoses or piping that was not sanitary.
--- In STMFC@..., "Gatwood, Elden SAW" <elden.j.gatwood@...> wrote:
<snip> One was to repaint with different wording or minimal
lettering. One might have been simply to write "inedible" on the end...maybe