Looking for other words to this. Some start 'Gentlemen should please refrain....(my wife remembers only part of that one!)
.
The one I know is

When the train is in the station , please refrain from urination
Have respect for Railway property
If you really must pass water, go and find a Railway porter
He'll direct you to the lavatory

And just had this from my friend John Wright in France

Passengers will please refrain from copulating on the train
While standing on the platform here at Crewe
Please restrain this natural function 'till we get to Clapham Junction
Where you'll find there's f**k all else to do

Splendid!

There must be many more versions - please share them with me to add to my collection of 'Parodies and Silly Songs'....my friend Baz Parkes once described me as having ' A head full of shite' !! Fine by me.....

Thanks Dave