What are these marks on the harmonic balancer?

[1967RS/SS]

Trying to find TDC on my 350 (without a piston stop tool) and found these paint marks.  If I rotate these to 0 will that be TDC?  If not, what are they for?   

[CNorton]

That's one-half of what you need.  The other half of the equation is the "0" or "TDC" mark on the tab.  Theoretically, when the line on the damper is directly aligned with the "0" mark, the engine is at TDC.  It is not, however, certain until you confirm the true TDC with a piston stop and compare that to the mark on the tab.

[69Z28]

The mark is for setting the timing as we all know and the white on either side of the mark is just to enhance that mark when the engine is running and the timing light is applied. Way easier to see the timing mark. A common practice that was done as far back as I can remember.

[1967RS/SS]

Ok, then do i just set those marks to 0 and that is TDC or would i need to still find TDC?

[z28z11]

You'll still need to verify whether the mark is on the #1 or #6 rotation - both valves on the #1 cylinder will be closed if you are at TDC for the #1 piston (you probably knew that, just a reminder). I've started engines before without realizing it; you usually find out quickly enough -

Regards,
Steve 

[69Z28-RS]

When the timing mark on the damper is at the 'TDC' mark on the pointer, the piston is always UP at TOP DEAD CENTER, .. BUT.. 
1) the piston might be UP on Compression (which is the one that counts for timing), OR
2) it might be up on Exhaust (in which case the exhaust port will be open). 

Just pull the LH valve cover and observe the rockers as you rotate the engine thru the 4 'strokes'  (intake, compression, power, and  exhaust).  If you've never done that before, it will give you a new appreciation for the engine operation.. ..  and don't forget that the crankshaft is rotating twice per rotation of the cam, and that makes ONE cycle of the engine.