Halt tells Will that he and the Baron purposely read the note in front of Will, then specifically said where they would be placing it. They wanted to see if Will could figure out how to read the note, if he'd have enough curiosity to want to obtain it, and if he could remain concealed in the shadows without being seen. Someone that becomes a Ranger must be able to be silent, think on his feet, and be curious. All of which Will is.
