Engine Tag What is it?

Yea i just bought a 1985 Iroc-Z with an engine that has a small rectangle tag on it that has the number 58051 i was told its a remanufactured motor and thats the serial tag for it i was wondering if its true and if not what does it mean?
Thanks
Dave

believe half of what im going to write, but here it goes.......
I dont think its a serial # "tag" because if its a "tag" then you can easily take it off and it would defeate the porpuse of an engine having a serial # tag. Or, maybe the guy who re-manufactured that motor must have type of inventory control on the motor they rebuild. And maybe it is the # so and so that came of the assembly line at some GM plant. Thats all that come to mind, maybe some of these guys here that really know what theyre talking about can tell you exactly.

a picture or a better discription of the tag and what's on it could help