1 cam: for the original Leicaflex
2 cam: for the Leicaflex SL & SL2
3 cam: for later R models
ROM: for activating some functions on the R8 & R9
Contacts mean a ROM lens.
2 cam lenses have 2 silver coloured "ramps" around the rear element.
3 cam lenses also have a 3-stepped black ramp in addition to the silver ones.
1 & 2 cam lenses have a more limited market.
Short version, if they meter at full aperture on an R3 - R9 body, they are *not* 1 or 2 cam lenses.
Apparently there are also "3rd cam" lenses which only have the black staggered ramp & not the silver ones (not useful for Leicaflexes, as are the ROM ones).