I've noticed 3 random long dark marks on my body, what could this be? (photos)

Past month I noticed three random marks that came out of no where, no explanation. They all look very similar, just in different places ( inner thigh , rib cage, in between breasts ) at first I just thought they were bruises although they never really hurt, they are just very noticeable and dark in color all straight long markings. Should I be worried?

No doctor answers yet