2 Black spots on golden retriever penis

Just noticed 2 flat dark black spots on his penis and he seems to be licking it a lot.  He is 3 years old. Thank you.

Hello! - anything skin-related that involves repeated licking is a concern, because dogs can sometimes lick themselves raw and leave themselves prone to infection. In general cancer is less irritating than skin infection, so I have hopes of your vet finding the latter, but it always pays to have them check and, hopefully, help to prevent the licking. Please do let us know how you get on.  

I trust that these are on the skin of the penis?  Are you able to tell us more about what they look like?