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Joined: Jan 1970
Sometimes an original owner will engrave his initials or social security number into the case. If the US government was the original owner there will most likely be some type of label on the machine or serial number engraved into the case for inventory purposes. If there is no evidence of any of this, it is likely that your 11C was originally purchased by an individual, not the government.
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I don't know about the HP-11C, but there were a few HP-35's that were engraved with the initials A.E.C. (Atomic Energy Commission) and some HP-35's had a silver "Property of the U.S. Gov't" sticker on them.