The symbols are actions the player needs to take while reading and playing the tablature. (see below) Tablature is a method of musical notation often favoured by guitarists.

Tabs Symbols:

() Optional note
/ Slide up
\ Slide down
h Hammer-on
p Pull-off
pm Palm Mute
v Vibrato
+ Harmonic
x Mute note
b Bend
br Bend release
pb Prebend
pbr Pre Bend release
|| Repeat Strum/Picking
R Repeat Section