A couple of other things you mentioned above:
ORV trails and routes are marked with orange triangles (in some areas with a square yellow backing), and are printed with ORV Route, ORV Trail, MCCCT, etc. Routes and trails should be marked every 1/10 mile or so, and should also be marked clearly if the route/trail turns, crosses an intersection, etc.
Snowmobile trails are marked with an orange diamond.
The confusing thing is that many of the ORV routes overlap snowmobile trails, and may have both sets of markings. Also, many of the snowmobile routes follow forest roads which are legal if you are SOS licensed.