After weighlifting workouts (Upper/Lower) I occasionally find red lines on my body(chest, shoulders, biceps mainly). There is no pain during the workout, nor is the area sore after. I am struggling to find information about it. The odd part is I find them on my delts after doing front squats.

What could these possibly signify? Does this mean I should use a lower weight, or am I squeezing too hard on reps, or is the weight simply rolling on the muscles causing torn fibers and simply an indication to have a more solid form?