In my experience, many passengers, after they've woken up at 5:30am after a night of packing, getting stuck in traffic, stressing about the time, getting lost in the airport, having their hair-gel taken away from them at security, running to the gate, worried they've lost their passport three times, by the time they get on board, combined with a little less oxygen and a G&T, they do come across a wee dense and say the darndest things.
As for the "another sign" proposal, not everyone speaks English and most people are too busy texting or talking on the phone to notice anyway.