I collect all sorts of celebrity signed checks, not just baseball.
Here are a couple that might be of interest to people here at the Net 54...
This is a 1983 check from Hall-of-Famer and Mets broadcaster Ralph Kiner made out to "Kiners Korner Inc"...
(For security purposes, the routing number has been digitally removed from this image.)
Here's Kiner's handwritten endorsement on the back of that same check...
Finally, a 1961 Casey Stengel check with a reference to the New York Mets in Stengel's own hand - six months before the team ever played a game! This check was written October 12, 1961, two days after the expansion draft in which the players who would comprise the inaugural 1962 Mets were selected.
Unfortunately, bank cancellation holes go through the handwritten words "N. Y. Mets," but it's still a pretty historic piece, I reckon.
I've got a number of celebrity checks (not just sports) scanned and posted on Flickr, and if you're so inclined you can check them out
here.