I don’t know what this is, but I suspect it’s not anything too serious. One question - how old are you? For some of us, just getting older can cause a lot of brownish spots to appear on various parts of the body, altho I can’t say for sure whether that could include the penis. I would suggest seeing your regular Dr 1st, then possibly either a Urologist or Dermatologist, possibly both. Please check back here & let us know if you find out what this is - I’d like to know myself & Im sure others who may have a similar issue would like to know as well...