It's likely part of a warranty label that was applied to the CPU by an computer store/builder. Back in those days, particularly when CPU's didn't require heatsinks, it was common practice to stick a tamper-evident label over the socket and CPU to indicate removal. CPUs were a high value item, and the labels were used to prevent claims of people who didn't know what they were doing, removing the CPU, bending or breaking pins, and then claiming warranty on the unit.