Just learnt of this from someone in Edinburgh where it is apparently working well and it's in some other cities too. The idea is you contact the city's branch with the location of where you were harassed and what was said and one of their volunteers goes and chalks the words onto that location. They take photos to document it too. Such a simple but effective idea to highlight how pervasive harassment is, especially where some sites are collecting several writings, and a lot are from school girls too.
Edinburgh Instagram page
www.instagram.com/catcallsofedi/
Organisation's website
www.chalkback.org/