Here are two signs communicating the same message: that the reader is approaching an environmentally sensitive area. I have come across both while entering forest preserves.
The first sign is effective, as it says just what it means to. But on a blue highway sign amongst all the others on the road it could be easily overlooked or forgotten. Perhaps the driver is looking for the exit, minding his speed, as well as trying to drive. He may not even read the blue sign, which many drivers know are usually reserved for rest areas and food or gas. The highway is not a place for supplementary information. I know that the sign contains an important fact- but a quick glance at it will not leave the reader feeling terribly responsible for his actions while in the area.
The second sign is clever and amongst the terrain it attempts to protect. It is much more effective as it directly addresses the reader. This alone tends to grab attentions better but it also uses a clever play on words. It contains the same message but is much more memorable. It also makes very clear that the area must not be disturbed. Your presence must be very minimal while visiting.
Neither sign mentions any sort of environmental consequence. This is an additional piece of information that can make people listen. I know the highway sign has little room for it, but within the state park the second sign could have some sort of information pertaining to the wild plants and animals. This is often not enough though. For instance a personal financial consequence could be instated: if they are caught littering or disturbing the area then they will be forced to pay a fine.