I appreciate warning signs that actually get your attention.
If this sign just said “Danger: Do Not Enter” that’s not very specific. Why is it dangerous?
I’ll quote one of E.B. White’s rules of style: “Be clear.”
“Muddiness is not merely a disturber of prose, it is also a destroyer of life, of hope: death on the highway caused by a badly worded road sign, heartbreak among lovers caused by a misplaced phrase in a well-intentioned letter, anguish of a traveler expecting to be met at a rail station and not being met because of a slipshod telegram. Think of the tragedies that are rooted in ambiguity, and be clear! When you say something, make sure you have said it.”
There are two reasons not to enter: the fall, and the croc. Be clear about it.
(You can tell I’m an English major, because everything relates back to The Elements of Style.)