Railroads employed "date nails" to mark the last time ties were replaced. I have only come across these relics on what is now the CN Iron Range Sub and in Two Harbors outside the museum. The most recent found was 62 for 1962. Apparently, when steam engines left the Missabe, date nails went with.
All those shots of interesting railroad details, what you see trackside, up close and personal! Excludes shots going into my other albums: "Engine Details," "Signal Details," and "Switchstand Shots."