Hah! that's great that you can tell it's high-E just from the sign.

Someone spent some time creating this work of art so I expect there must be a good story behind it. I doubt it's official so I won't be surprised if it's removed.

My best guess is that someone's belayer for the last pitch of high-e did not anchor in, dragging them both to the ground when the leader fell, or causing a nearly fatal accident, and that is the impetus behind the sign. Although i've never heard of this happening so it is probably hogwash

Dana Bartlett knows the story - see the comments under the route.