Maybe certain other Deathly Hallows symbols will now light up in Harry's presence, especially if there is a lost storehouse of some sort with a similar mark.

If it doesn't end up being important, it could just be whatever enchantment is on the Peverell gravestone that makes it recognize someone's anti-Death resolve (possibly only if they're a Peverell descendant) and recite the prophecy, pointed out in the narration so the reader knows where the prophecy was coming from.