When walking on the streets on NYC one will come across many different types of pushcarts selling breakfast, roasted nuts, lunch etc… Most of the carts are located in densely populated areas where thousands of people walking by them each day. Why not monetize the sides of the pushcarts with advertisements?
Ideally the best way to make revenue would be to buy the rights to the space on all the pushcarts from the pushcart owners, then sell the ad real-estate to agencies.
Working with the Government
Since NYC officials give out the licenses for the street vendors, the city might be picky about what the vendors are allowed to put on their carts. I believe a smart way to please the city officials would be to offer one month free advertising, for each ad unite, to specific government non-profit organizations. Additionally, these ad unites should provide some social good. One month out of the year should be dedicated to providing value to NYC residents. An example would be Word Month- where each ad unit would present a interesting word along with a definition. I believe combining free advertising to government non-profits and providing social benefit to the ad unites, will significantly decrease the probability of government intervention.