From the picture it looks like a birth mark. Yes, you can have them on your penis. But, I am not a medical doctor. And, yes, you can get penile cancer which is more common on the head. I certainly think it's something you should point out to your doctor.
OMG..i have the same thing on my penis. I think the first time i noticed it was somewhere around the time i began puberty like at 13 maybe. It doesn't hurt and it isn't raised above the skin. Its like i just got a big freckle. I'm not sure if it could be cancer b/c i've had it for years..and i dont have any history of cancer in my family. I imagine it is too embarrassing to tell anyone as it is for me. I dont even know what kind of doctor you ask about this.
That looks like a birthmark. Penis cancer is extremely rare, and your mark does not have any of the traditional signs of cancer (irregular border, bleeds, changes color, etc). But I agree with PaulK9378, you should point it out to your doctor the next you go in for a visit - it will give you peace of mind, and it's not a bad idea to keep an eye on birthmarks, moles, etc.