Hmm, the best I've done is finding an oversized paper currency (I have
forgotten the denomination) under the plate of a square grand I was
tuning for the local historical society.  I was cleaning the soundboard,
with a rag on the end of some spring steel, when this bill flipped out
from under the plate.  The historical society had it appraised at about
$750, although I think they put it in their collection.

The fall out from that happened a few years later when I applied for
the job of curator assistant with them, and one board member said,
"Well, he's an honest guy -- he gave us the paper bill he found in the
Ehamann home piano!"  That was my first paid museum job, which led to
the others.

David Dewey
Oroville, California