Abnormal moles are a sign of melanoma skin cancer, according to the American Cancer Society. Unusually shaped or textured moles or moles that change in size, color or shape may indicate the development of melanoma.
Normal moles are usually brown, tan or black, may have a flat or raised appearance and may be oval or round, notes the American Cancer Society. Moles or skin spots that change in symmetry, with one half not matching the other, or that have notched, blurred, ragged or irregular borders may indicate melanoma. Moles and spots that are more than one color or larger than the size of a pencil eraser require evaluation by a dermatologist or other medical professional.