I have a red burn like vertical line on my right shin. i have no clue how i got it. i havent hit or scratched my leg at all and i dont shave so it cant be from a razor. it doesnt hurt. what can cause a mark like that?

All people sometimes have minor injuries, scratches, etc that they don't remember or didn't feel at the time, so that might be the problem. If it becomes painful, or grows, or if you develop other symptoms like fever or a tender lump above it (like groin, inner thigh), it could mean lymphangitis, a sign of infection. If so, see a doctor soon; or if it doesn't clear up in a few days.