I found these two articles helpful:
http://www.stdpanels.com/information...-on-the-penis/
http://menshealth.about.com/od/disea...enis_spots.htm
Basically most spots are rather harmless and often mistaken for something else. If you want to be safe, visit a doctor.
Anyways, if you are participating in these kind of activities, you should be mentally prepared for shit to happen.