Hypersmurf
Moderatarrrrh...
I suppose you could do it if the symbol was unattended, and royally screw him over, but if the cleric was holding or wearing it, I wouldn't allow a "called shot" at the holy symbol any more than I'd allow people to aim for a wizard's spell component pouch, or to let them try to hit him in the mouth and sever his tongue... That way lies cheese.
So what are the rules for "Strike a Held Object" in the Combat Section for?
-Hyp.