The best thing about melanomas (and there ain't much) is that they don't hide very well, so they can be caught really early. We don't have any medical treatments for melanoma, except early recognition and excision of these very malignant, very metastatic lesions. The only way we as dermatologists can treat them is by cutting them out early, before malignant cells spread to lymph nodes and other parts of the body.
Most people notice moles that have been with them for a long period of time, most likely its always been brown, regularly-shaped, and flat. If one of your moles starts changing and creates a black corner or center, then you should get it checked out immediately. If you experience any changes to a mole such as a slight raise, color change, or new symptoms like itching or pain, get it check out immediately to ensure there's no burgeoning melanoma.
Those are the first signs of this very important, very deadly type of skin cancer. A matter of a month or two can make a difference between a stage 0 melanoma that's barely penetrated through the epidermis and a stage 1 melanoma which is headed towards lymphatic vessels and the bloodstream where it can spread. Early recognition is key for melanoma, so always be looking for changes.