RIFT's newest patch, 1.02, includes a new feature designed to fight precisely that dreaded eventuality, with the new "Coin Lock" system restricting use of a character if the parent account logs in from a different location. While locked, the characters cannot access the auction or trade functions until the player verifies his or her identity.
While the system is a great idea in theory, several players are reporting that the coin lock system is not working as intended, with supposedly "locked" characters remaining accessible and capable of using all features freely. There are also several threads devoted to claims that account hacks are still taking place, although as with any account security issue, culpability is difficult to determine. While RIFT's Coin Lock is an excellent idea, it remains to be seen whether it's actually accomplishing the stated goals.
[Thanks to Simon for the tip!]