Red line going across my stomach?

I see it. You look fit. It could just be a 'gym issue'. You might have been doing too many ab workouts.

Or it could even be your position. Maybe ur lying down a certain way for too long and causing your muscle to ache (if you have abdominal muscle ache then this is a sign).

Another cause could be 'tight pants'. This would occur if you wear your pants relatively high with a tight belt.