Timing marks CAN YOU TELL ME WHAT TIMING MARKS ARE ON MY CITROEN C3 1.6 16VALVE

You need locking pins for both cam shaft pulleys as well as for the crank. The cam pulleys each have a hole in them which line up with a hole in the cylinder head through which an 8mm bolt cam be used to lock them. If you are looking at the cam pulleys from the RH fender side, the LH pulley hole locks at about 5 o'clock and the RH pulley at about 7 o'clock.

The crank locking pin is in an awkward position and a bit difficult to access. the hole is behind the oil filter housing and the pin locks into a hole in the back of the flywheel.

Please note that if your cam belt has snapped this engine will bend valves. If it is a scheduled belt change then it is quite easy to line up the marks and do the belt replacement.