There is only a slight clearance between sides of cars and signal-towers.

IF YOU EXPECT TO SEE THE NEXT BLOCK KEEP YOURS INSIDE.

There was another one worded as follows:

YOUR HEAD MAY BE HARD
But not so hard as Bridges and Tunnel Arches.

Railway company will hold you responsible for damages to bridges and tunnels and signal-towers—they are not insured.

KEEP YOUR BLOCK INSIDE

And yet another:

Huns are waiting.

Trenches ahead.

Speed up.