-Gonorrhea, white smelly secretion from the urethra.
-Chlamydia, pain in the testicles and genital area.
-Syphilis, it depends on the stage we are talking about. The first stage is known because of the chancre. There is normally only one and it appears on the area in which infection took place. After a few days, chancre disappears and the patient develops a rash along the body, specially in the hands. Both chancre and rash are highly infecting, and there can be infection even just through the contact skin to skin having those lesions. It can be transmitted even when condoms are used.
-Herpes, big blisters on lips or genital area. Also able to infect through the contact skin to skin.
All the best.