I am not sure that the level of accurate comprehension is as high as one would like when it comes to interpreting this sign, which is similar to one we saw in the Mount Baker National Forest. I assume that the public is to read it as "speak before approaching horses from the rear," and it probably has something to do with the ranger's desire to keep horses from spooking and killing people on the mountain trails. I parsed it, initially, as meaning "beware of horse farts," and then as "listen to a horse's ass."
This is my proposed alternative: a text sign, reading "Speak before approaching livestock." Lower humor value, but more lives saved in the end, eh?