At least two interpretations of the words on the banner demonstrate that the sign advocated the use of illegal drugs.

Deterring drug use by children is an important interest held by schools.

Dismissing the banner as meaningless ignores its undeniable reference to illegal drugs.

Political speech is at the heart of the First Amendment and, thus, can only be prohibited if it substantially disrupts the educational process. (Tinker v. Des Moines (1969))

If the banner would have been set up outside of a school event, it would have been protected by the First Amendment. (Bethel v. Fraser (1986))

Schools may regulate some speech even though the government could not censor similar speech outside the school. (Hazelwood School District v. Kuhlmeier (1988))