I'd suspect one mark would be TDC (top dead center) to adjust valves with the other being BTDC (before TDC) to adjust the points.
(I am assuming the 'G' is a gas engine.)
An image of the markings would be helpful, one might just be a casting flaw or rating.
Mine, from after Mitsubishi took over Satoh, is the inside mark on the pulley. I attached the capture from the service manual for mine - if it's the same the second mark, it is the IT mark. I am guessing IT is the start of the intake stroke.
You can also pull a valve cover (guessing yours is diesel) and manually turn the crank until the first rocker is highest and then verify your marks (only if you have already drained the oil).