Hello,
It looks like bruise penis. Penile bruising can be due to trauma, sexual intercourse, masturbation, sexually transmitted disease, penile injury, skin entrapment in clothing etc. Normally bruising due to non infectious causes would resolve within 8-10 days. Maintaining good genital hygiene, using soft underpants would help. See a urologist if bruising persists after 10 days.
I hope it helps. Take care and regards.
It does just look like a bruise. Keep an eye on it and if it doesn't go away in a couple of days or gets worse contact your doctor. Do not take any blood thinners as this can make internal bleeding worse (ie asprin).