This is one of the best public pranks ever.
Use a super glue, Liquid Nails or another very strong adhesive and glue a quarter to the sidewalk. It's really easy to do, it sets up in seconds and the fun lasts for hours.
Watch well-to-do people try and scrape it off the sidewalk. Try finding a location where there is a little irony of someone trying to pick up the quarter. Outside the entrace of a Nordstrom store, a Macy's, or just a bank.
Or go for the gusto.
On your next trip to New York City, Washington, DC, bring a roll of quarters and commence with the gluing. Choose a target like anywhere on Wall Street, Madison Avenue, the Disney Store in Times Square. How about the steps of Congress? Perhaps the entrance to the Pentagon?
A friend of mine used to glue a quarter all the time to the outside of his office. It was great fun to watch a business man in an expensive three piece suit kick at the concrete for a few seconds to dislodge the quarter. His favorite story was one kid that worked for 10 minutes to get that quarter loose. The entire office was watching this kid desperately kick, claw and jimmy at the quarter. Finally the quarter came loose and everyone in the office cheered. How often do you see a kid work like that these days?