2012 Washington DC, USA
When students conducted water monitoring on a tributary of Sligo Creek, they were troubled by the extent of trash evident in and around the stream, and they decided to carry an anti-litter message through the neighborhood with anti-litter signs. They contacted the city government to obtain permission, and mapped out where to place the signs throughout the neighborhood for best effectiveness.
They designed signage online, and had the design produced as durable metal signs.