Meaning trumps linguistic precision on sign

Second language learners share an unconscious assumption that L2 must follow the rules of the native tongue, which of course, it never does. Linguists call this first language interference.

That's why adults who learn second or third languages usually make typical L2 errors.

Whoever created this sign didn't bother checking the precise English wording or spelling. They were confident in the sign's ability to convey the meaning, which is clear, in spite of the obvious mistakes.