It's either the relic or its a key, remember Ozpin is the wizard in a past life he created the maidens, who's to say he was using the Relic? besides, why would he have something that valuable in plain sight where he knows someone may take it off his body, should he (or Qrow) be taken by surprise, the fact that he was expecting this, allowed him to send it elsewhere. If it's a key, it could be disregarded as obviously not being the relic therefore useless, if some piece of it is the ONLY way to access the relic, however, not only is it incredibly valuable, but it also gives a reason for an eventual return to Beacon, in addition If the Relic is at beacon but they can't find it without the key, he thereby redirects much of Salem's forces (grimm)to the school, meaning there are fewer available to stop the people of Remnant from regrouping or for her to use to take the other schools, at least the primordial grimm like Kevin the Dragon and the ancient Goliaths, right now a large portion of the Grimm in Sanis (continent Vale and Vacuo are on) are in one place, if Oscar gets the relic from Beacon, using Ozpin's knowledge, they may be able to wipe out all the grimm there, as to how they'll get in, remember that tunnel in the cliff from the Nevermore fight in Vol1? The best we can tell it heads under the school itself, now if I were to hide an object that I knew my enemy wanted to get their hands on, I wouldn't put it in the obvious "Look Here" Beacon as strong of a defense it may provide, I would hide it someplace obscure that would have the defenses from the school, but wouldn't be easily accessible from there, also remember where Oz put the chess pieces/ "relics" not only would grimm be cleared from that area yearly, but it would be one hell of a way to leave a hint as to where to start looking, one that would seem logical rather than just listening to some voice in the head of some random farmboy turned huntsman from Anima. What's more is that Salem couldn't recruit from Beacon itself, or have them pose as Beacon students, so they wouldn't really know about the initiation, or at least not the exact location, further concealing his play at this game of chess. Its safe to assume that every action Ozpin took was deliberate, Oz enrolled Ruby, encouraged her to get involved, and gave her one HELL of a hint as to his nature, he enrolled Blake, basic background checking would have revealed her past, and connection to the White Fang, he probably calibrated the catapults so certain teams would form, or at least be more likely, easiest to do with Ruby and Yang, being sisters they would choose the same chess piece to be together, thus bringing together Weiss and Blake, two people who's backgrounds couldn't be more different and indeed keep them from associating with eachother, fighting side by side, Oz is one for symbology, as it can prove a very powerful tool, what a better way to represent the responsibility of remnant's people to unite as one?