Stamp Cover or Currency Cover?

I have several $2 bills, series 1976 , crisp unc. with USA Scott # 1596 stuck on RH side. The LH side is Postmarked Evans LA. April 13 , 1976. Is this some sort of prank? Should I treat this as a stamp cover or some sort of currency collecting freak? The envelope they are stored in says " $2 bills First Day" Can anyone help me?

Greetings Mr. Curry.
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letter inquiring about the same thing in the Collectors' Forum (except the two dollar bill was postmarked Maywood, Ill and had a Scott #1597).
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The Linn's response was, in part, as follows:
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"The series 1976 $2 bill was redesigned and printed in a quantity of
590,720,000 as part of the bicentennial celebration. ... Someone got the bright idea of creating bicentennial collectibles by affixing first-class postage stamps to the $2 bills and having them postmarked. We don't recall whose idea it was originally, but the practice was carried out at post offices across the nation. ... " .
Their response doesn't say how many of the bills were stamped and postmarked. Nor did they classify what type of collectable. Personally,
I'd call them exactly what it says on your envelope, " $2 bills First Day [of Issue]". What do other rcsd'ers think?
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I'll try to keep an eye on the Collectors' Forum to see if there is any follow-up. Also interesting is that the guy who wrote Linn's asking about the two dollar bill picked his up at his local bank from their regular cash drawer. So, there just might be more of them circulating around out there.
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Gordon Lee
Great Fritain Royal Memorabilia & Three Dollar Bill Emporium
I like stamp collecting and I'm sticking (glue or self-adhesive) to it.