My mother sang

Passengers will please refrain
From flushing toilets while the train
Is standing in the station, I love you.

She taught it to us while on a train trip, during which we saw such a sign in the train's restroom.

Mom, who was, by the way, nearly always a perfect lady, also claimed to have seen a sign in a rest room that said:

When using our john, please dont't stand on the seat.
Our crabs can jump up to 18 feet.