Chalking techincally isn't criminal damage, source > https://academic.oup.com/cardiovascres/article/116/11/1910/5770885 also check out this vid by Stephen Fry https://www.youtube.com/watch?v=-ZBzkOwohMs
Yep, me and some peeps are planning on some chalking soon too.
Of course rules can change by country and municipality in some cases, so always be sure to check if it's okay where you're planning to do it.
This is not me saying 'don't break laws', but be sure to know you what the laws are and what rights you have :)
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