Whatever it is, just don't do it, okay?

I have no experience in traffic engineering, but it seems to me that the one overriding concern when designing a road sign is not only visual - but also syntactical - clarity. The sign itself is simple enough with it's basic yellow, black, and red on a white background, but the intended meaning has me completely befuddled. Just what exactly is being prohibited here? (And remember folks, ignorance of the law is no excuse.) Construction of signal fires on taxis strictly prohibited? This is a roof-mounted nuclear device free zone? Something about transporting giant jellyfish on 1950's DeSotos?

I love public displays of unintentional ineptness/confusion. It warms the cockles of my heart. This sentiment is not a Freudian thing about feeling superior; it's just a constant reminder of human frailty (which I can certainly relate to).