For those who haven't tried a rally, here's a peek into reading this page from the Dakar Stage 1 roadbook.
! = Hazrard
!! = bigger hazard
!!! = You can die here
P = Piste = the road or trail
S squiggle = twisty road
E3 = narrow
Down arrow = down hill
Up arrow = up hill
+/-V = road or trail is hard to see
WPM = Waypoint Masked (hidden waypoint you must pass through, sort of like a Baja SCORE VCP, but it won't show up on the GPS until you're close to it.
SER - Tight/sharp turn
There are about 75 symbols and abbreviations like these that the rider/navigator needs to memorize.
Each competitor has their own way of marking the roadbook with colored markers, to help read it quicker and more efficiently.
The first roadbook entry, at KM 138.45, basically says "watch out, the course is twisty, narrow, hard to see and goes down hill".