I couldn’t find anything under Title XLVI CRIMES, Chapter 806 of Florida’s laws allowing teachers to give the ok to students to engage in graffiti.
(1)(a) A person commits the offense of criminal mischief if he or she willfully and maliciously injures or damages by any means any real or personal property belonging to another, including, but not limited to, the placement of graffiti thereon or other acts of vandalism thereto.