There is only one mark, which should be TDC (unless someone has assembled the pulley wrong).
The advance curve starts really low on these engines, making it difficult to accurately set initial timing with a light. My suggestion is to start at about 3/16" from the TDC mark (which is about the 4 BTDC called for in the book), and then advance it a degree or two at a time until you can just force the engine to ping a little, by using heavy throttle at low rpm (30 mph in 4th gear) with the engine thoroughly warmed. Then I like to back off by about 2 degrees (half of a hash mark on the distributor vernier), just to be safe.