As his business card. Sure, it’s old news if you keep up with news on Will Wright, but for newcomers that may not know, when you meet him in person, he’ll give out foreign money as a way to contact him:

But Sim City and Spore creator Will Wright’s got us all beat—he puts his personal information on actual printed money. Sure, it’s Yougoslavian money that has no longer has any actual value, but if anything, that makes it cooler.

I still have the old Nghia Viet Nam 100 Mottram Dong Bank Note he autographed and gave to me when I met him tucked away in my wallet. Can’t believe it’s been…what, nearly 8 years or so? LOL.
Via Kotaku