Fortunately, it's not the kind of magic that could really be deciphered from a surface examination. It would probably require a detailed examination of the enchantments to learn about it in-depth. I suppose it's more accurate to say that they would put a stone in a guarded, known location for the respective factions to use, rather than just giving them a stone outright. They would easily be able to learn that the stones connect two fixed points, and they require a key to use.