Ad for security glass uses real money

According to 37 signals, the money sandwiched between the shatter proof glass in this bus stop ad is real.
Link (Thanks, Itchy!)

UPDATE: Gerald says: a note on that bus ad; it's in downtown Vancouver and the top layers of money are actual Canadian $20 bills and the rest are fake, like the ones in movies. There's still a hefty chunk of cash in the ad and the bus shelter is actually monitored by video by the ad agency (which is conveniently located across the street).