Notes to strangers
Moss graffiti
https://www.instructables.com/id/How-to-Make-Moss-Graffiti-1/
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I’ve seen these around, v simple and easy. Use sticky back plastic so mine don’t run with the rain so quickly?
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Larger posters
http://destructables.org/destructable/wheatpaste-recipe-putting-postersbillboard-alterations
https://www.bombingscience.com/graffitiforum/threads/wheatpaste.3389/
to the touch 