From What is the correct resignation procedure? it is clear that, although FIDE has no special rules governing on how you resign, it is common to either offer your hand or make some sort of exclamation (i.e. "I resign!"). What is important is that your intention to resign is unambiguous.
Now, the rivalry between Kramnik and Topalov has gone to such an extend that each player refuses to shake the other's hand or engage in any kind of pleasantries. Which raises the question - how do they go about resigning when playing each other without creating confusion about their intention?