If you're not sure, just whip out No.1 (or 4) spark plug and drop a long screwdriver down there. Turn the crank slowly to carefully determine where TDC is.
The 'dot' on the crankshaft sprocket (at roughly 6 o'clock in your photo) should align with a mark on the outer casing.
In a piston engine, top dead centre (TDC) is used to determine the position of a piston in which it is further from the crankshaft. This is used to determine when to generate a spark. Many Renault models appear to experience problems with the TDC sensor, but it is a simple and inexpensive part to replace.
Currently in S80's garage: Megane I Phase 2 1.8 5dr
any ideas what mark should be on the top, i have found the marker on the cam pulley but on the head there is a green dash of paint and slightly to the left you can see remnants of a white paint dot over the top of the N impressed in the head casing. the two marks are very close but proberbly a tooth apart