Some engines had these tags as an alternative to the stamped shroud or standard serial plates. However, if you blew your engine and the dealer ordered a replacement, they'd only order a shortblock (all of the internals, but the head, flywheel, stater, and blower housing were missing). These shortblocks had a little aluminum tag bolted to the engine block, usually on one of the top sump cover bolts. They'd transfer all the other parts from the original engine and you'd be all set with a "newish" engine.