I think there might be a reason for such a dumb sign. It's either this, another reason, or the fact that, again, someone is really good with Photoshop.
One day, someone made a sign that used the same materials and edges as the one in the avatar. Someone cut themself on the sign, and sued the person who made it. To prevent this, the sign in the avatar was created...only the fact that people can't read the part about the bridge being out ahead kind of ruins the point of making the sign.
You know, I should make a sign like that, and put it up somewhere....now THAT would be funny!!!