At this point, there are a number of items that can be identified through exploits. That is, items that can be identified by the fact that they give a message or react to the user interface in a way that other similar items don't, even though the PC couldn't possibly tell the difference.

Chief amongst these is the Ring of Djinni Summoning exploit. Although as far as the PC is concerned, it is just a ring like all of the others, if the player has the PC go to the overworld map and tries to 'U'se the ring, it informs them that you can't use it in the overworld map (I believe it says "Not Here", but I could be mistaken). Other rings suggest that you try to wear the ring to gain any effects. As a result, the player is able to identify a ring to be a Ring of Djinni Summoning, even though the PC couldn't possibly know that the ring is more 'U'sable than other rings.

In this particular case, it is easily solved by simply having all rings say "Not Here" if you attempt to 'U'se them on the overworld map.