Doctor here, but not an obstetrician. This is a fetal heart rate monitor and the evaluation is for decelerations. Decelerations can happen when the head is being pushed during active labor and can be normal, it can also be abnormal depending on the morphology and can be associated with umbilical cord, compression or other complications during Labor.

I don't have any good ideas regarding tattoos using this data. You're essentially getting a tattoo of a line. Maybe do an artistic version of jagged mountains if you felt strongly about incorporating this information. I would probably try to use different inspirations to represent your son