Now if you follow the Star Wars Rebels cartoon, you know that this look is actually dated. Sabine Wren customizes her armor... and hair... as she goes. Each new mark signifies a major battle or campaign. In essence she's keeping score on her armor - just like Clone Captain Rex did - but in a less morbid manner (Rex kept a tally of the dead on his armor).
The current incarnation of the Lothal Rebel's ace saboteur and demolitions expert currently sports a silver to violet mane of hair (She had blue to green hair in Season 2), and a much more colorful set of armor. This is her Star Wars Rebels Season 1 incarnation.
Also she now wields the infamous Darksaber - the sword wielded by the late commander of the Mandalorian Death Watch, Pre Vizsla - who wielded the Dark Saber till Darth Maul decided to decapitate him. Darth Maul would wield the Darksaber till he decided to leave it in the Nightsister's lair on Dathomir where it would work it's way back into a Mandalorian's hand.
MORE AFTER THE JUMP