When we think of skin cancer, we first think about lesions that appear on the face, legs or arms. But, even though rare, skin cancer can appear below your nail. Bob Marley, a reggae superstar, died at the age of 36 from melanoma on his toenail.
Melanoma of the nail beds, called subungual melanoma, is more common in darker skinned individuals. According to Dr. Oz is occurs most often in African Americans but can occur in anyone. It usually appears as a dark stripe or band through the thumb, index finger or great toe. The dark band can extend into your nail fold or cuticle While every dark band or spot under your nail is not cancerous, it is important to get it checked by your doctor as soon as you notice it.
Other signs to look for include red streaks that do not go away. These may indicate squamous or basal cell carcinoma. Warts around your nail bed that won't go away with treatment may also be a sign of cancer. In addition, if you notice other changes in your nails, such as thickening, the nail lifting from the nail bed, grooves in your nails or pain, you should contact a dermatologist for an evaluation.
Nail cancer accounts for about 5 percent of all diagnosed melanomas but account for 30 to 40 percent of skin cancer in people of color. According to the Skin Cancer Foundation, "Sun exposure may cause permanent damage to the nail's growth center, called the matrix - especially the pale, 'half-moon' portion of the matrix visible at the base of the nail plate. Cumulative sun exposure may also permanently harm the nail bed and nail folds - the skin around the cuticle - accelerating their aging process and increasing the risk of skin cancer." 
Just as your face and other exposed areas need to be protected from exposure to the sun, so do your nails. Some nail polishes now contain UV filters.
The Skin Cancer Foundation also suggests the following to help protect the health of your nails:
Moisturize nail area daily
Wear gloves when outside in cold, windy weather
Never cut or push back cuticles
If you use nail polish, take a break periodically through the year for a total of 1 to 3 months
If you get manicures, check out the salon to make sure equipment is clean and sterilized
When doing self-exams, you should include both your fingernails and toenails and pay attention to any changes.
"7 Tricky Body Symptoms, Solved," Date Unknown, Richard Laliberte, Prevention.com
"Dr. Oz Nail Changes and Your Health," Date Unknown, Dr. Oz, HealthyBodyDaily.com
 "To Protect and Serve," Date Unknown, Staff Writer, Skin Cancer Foundation