But he wouldn't come out directly and say "Note the piano" - because there is no organic context/relationship between a pen placed on a piano. Q wants us to DIG to prove to ourselves (and, collaterally, others) that his drops are authentic - anon autist research FOUND a piano -AT- CD that MAY be Q's "Desk".
(The play-on-words of "Note" was a nice flourish, though, and - more than likely - was intended as a cryptic, post-discovery confirmation indicator)