The colored frame was an ACI label, for Automatic Car Identification, sort of like today's bar codes, only in color, too. It was a system to make interchanged rail equipment more quickly and reliably tracked, but eventually failed because the labels would get dirty or otherwise damaged in service. Scanning equipment was placed along the tracks, usually in yards, and also helped to eliminate jobs, the by-check clerks who would visually examine each car on an incoming train and record its reporting marks. The resulting list would then be compared with the computer printouts for the train to find any discrepancies. The ACI label was ultimately replaced by magnetic tags, which are unaffected by weather and dirt.