dropdrop

dropdrop allows you to leave a message or photo at your current location.”.
 Other people can see drops you leave behind, and you can discover drops near you. Want to plan a pickup game with your friends? Have something to sell that
 you need picked up? New to the area, and need some local tips? Everything
 on dropdrop is centered around location, so drops are relevant and timely.

Nothing you share on dropdrop has to last forever, and you don’t have to drop or comment as yourself. You can share drops only with your friends, 
or use stamps to post anonymously. All drops fade away eventually, and the duration, size, and audience of your drop is fully customizable.