if it's buddhist beads, it's a reminder to be compassionate and kind to others. it's also used to do silent chanting of sutra or mantra.
if it's more related to fengshui, then most probably for good luck and ward off evil.
u can see mark lee always wearing double beads. i think that's for hiao ka tong beh tiao metrosexual reason. anyway, no matter what he wears, he's one freaking ugly dick.