yeah i know there are timing marks, but everything else i've ever done has had marks on the belt that you line up with the marks on the engine as well. other wise you could end up with a different length between the sides than is needed, and put the timing out.
ie
a mark lines up with the mark on the bottom pulley, and one on the top, this ensures that when you put the belt on, you get the correct length between each mark,
every belt i've ever done has had this, from renaults and peugeots to subarus