Approximately a week ago i noticed something on my penis that wasn't there before, it was flat and a dark mahogany brown, what is it?

Here are some ...: What you saw could have been there lifelong and you just recently noticed it incidentally. Without a direct look at it, it's hard to give a specific answer. But, clinically, it may be just a mole. For now, observe if it changes its size, texture, elevation, or color over time; collect and bring those to Doc for review, analysis, physicals, and possible tests if being in doubt. Best wish ...