Sometimes a sign or object that is supposed to be serious and official, ends up defying logic, or being quite pointless. Like this sign. I saw it at the Duaringa airstrip in Central Queensland about five years ago.
My first thought was, what’s the point? By the time a pilot sees this sign, he’s already well and truly landed. Too late be worrying about liabilities. Maybe you are supposed to buzz the runway and read any signs before you drop in.