Yes that is correct they are tool checks, each person was assigned a number and issued 6 to 10 checks. Having worked in the tool crib in high school. the check was placed on a nailin the spot were the tool normally was. Since they each had a unique number assigned to only one person. The could also be used as in/out, tags. Generally they were used in dangerous environments foundries,smelters, mines, quarries, any place that could and often did result in death. They were often referred to as body tags by the workers.