on dohcs I have even made a mark directly across the two gears as well as on the head for foolproof indexing.
one or two more helpful tips, get yourself some of those black heavy duty paper clips. they will go over the belt and clamp it to the cams. get yourself one of those plastic springy woodworking clamps to hold the belt on the crank.
also when adjusting the belt, make sure you have it tight on the side the tensioner doesn't push on or it will go out of time.