"A Little Arrow Next To The Gas Icon On A Car's Dashboard"
"The arrow points to the side of the car your gas cap can be found on. If your car is older, or doesn't have an arrow, the direction of the fuel hose sometimes indicates where the gas cap can be found."
https://www.amazon.com/Panef-Corp-Powdered-Graphite-Lubricant/dp/B0016GZQ60
Now I don't use hairpins but I would think the side WITHOUT the sharp pointed end would be better against your scalp?