The 912E uses the same timing marks as the 1.8 liter 914 engine. Both used L-jet FI, so they used the same timing methods and marks. The D-jet motors (1.7, 2.0) set their timing at a different RPM, and set it to a different number.
Check this tech article
http://www.pelicanparts.com/techarticles/914_timing/914_timing.htm for details, and for a template you can use for making your own timing marks.
--DD