http://blogs.scientificamerican.com/cross-check/2013/12/17/from-my-archives-quark-inventor-murray-gell-mann-doubts-science-will-discover-something-else/

One final story about Gell-Mann: After our meal together in New York in 1991, I hired a limousine to take us to the airport, where Gell-Mann was catching a plane. Before we parted, he fretted that he did not have enough money for a taxi after his plane landed; if I could give him $40 in cash, he’d write me a check. As Gell-Mann handed me the check, he suggested that I not cash it, since his signature would probably be quite valuable. I cashed the check but kept a photocopy.