Minor variants rom a book I don't seem able to locate at the moment:

Passengers will pleas refrain
From using toilets while the train
Is standing in the station,
We thank You.

Constipation's recommended
While the train is being tended.
If the train can't go
Then why should you.

AND

Nothing looks much better
Than a young girl in a sweater
But the sweater may not be
What it a appears.

Boys, it's recommended
That you see what's IN THE SWEATER
Or your wedding night
Might end in bitter tears.

John