yellow arrow

"You post a Yellow Arrow because you have something to say about where it points. You thought is then forever tagged to that place. When someone else finds your arrow and sends the code, they get back the message you left on their mobile phone. Yellow Arrow is a symbol that means "there's more here: a hidden detail, a funny story, a crazy experience." Each arrow links digital content to real locations, creating a new map of what counts. When you post or find a Yellow Arrow, the way you see that spot will change. Get stickers and TXT shirts to join the global community of people, projects, and places."

from the yellowarrow.net