The Jewish Legal System: Laws of Damages: Defacing Property:
What is the source of the prohibition against defacing public property?
It is a violation of "bal tashchis", the prohibition against
destroying or damaging things, based on Deut. 20:19. See the
article on "Bal Tashchis" in the Talmudic Encyclopedia, Vol. 3,
which explicitly says that the prohibition applies even to things
that are ownerless.
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