I wonder how many have paused to consider the use of the verb. Have many even read the sign fully?
Is this a further argument that such signs are never read – they are merely scanned? Once an indication of the message has been interpreted, that is enough. This is more so when a clause separates the subject and the verb.
With the innocence of youth, I would have thought that some child might have told the Community Association that the sign does not (or even ‘do not’) agree with what is taught in school.