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).