Are splinter looking brown lines under fingernails something to worry about? there aren't any other symptoms present.

Trauma vs infection: The most common cause of splinter like hemorrhages seen through the nail in the ail bed, come from trauma. I've had them in the past from tapping my nails on the desk. I had to break the habit. Splinter hemorrhages as signs of infection are more often seen at the base of the nail near the cuticle. Again, the most common cause of these hemorrhages is trauma, even as minor as tapping your nail.