I was working at a game development company in the mid 90s that used Visual Source Safe and to avoid file corruption due to concurrent commits, we had a shiny silver baseball cap which you had to find and physically possess to commit.

After we had off-site devs, the physical cap wouldn't work. So the project had a "silvercap.txt" file and you had to exclusively check out . And of course people forgot to release that and work ground to a halt.