The accuracy of clinically diagnosing melanoma is about 50 percent.
A variety of pigmented skin lesions can simulate melanoma. Physicians should be very suspicious of pigmented lesions; when in question, these lesions should be biopsied and diagnosis must be confirmed by pathologic examination.

The external or surface changes such as bleeding, ulceration, scaliness, crusting, or an elevated area in a previously flat lesion are danger signs of more advanced melanoma.

Ulcer or ulceration is a secondary skin lesion, changes in the skin that result from primary skin lesions (suspected mole) and involves loss of the upper portion of the skin (epidermis) and part of the lower portion (dermis).
Melanoma ulceration is the absence of an intact epidermis (the upper skin layer we see) overlying the primary melanoma and has depressed center and elevated, hard borders. At the bottom of the center of the lesion can be seen secrets like pus or blood. Drying of the collection of blood, serum, or pus will result in crusting over the ulcer, forming a scab or crust.