Brandon leaked what it was after some puzzled it out, and fans deduced correctly where it came from. Apparently, its identity isn't any big time secret, it's doubtful Brandon makes a big deal of the identity in AMOL.

It's Hawkwing's sword Justice. Scholars found it in the water pool beneath the Hawkwing statue in the EOTW abandoned stedding and brought it to Rand.

It's not gone anywhere. Rand stopped wearing it for a while, you've missed Min noticed Rand started carrying it again toward the end of TOM.

We've yet to see its purpose, though.