Basal cell forum

SkinCancer.org has a great summary of the warning signs for BCC:

Warning Signs

The five most typical characteristics of basal cell carcinoma are shown in the pictures below. Frequently, two or more features are present in one tumor. In addition, BCC sometimes resembles noncancerous skin conditions such as psoriasis or eczema. Only a trained physician, usually a dermatologist, can decide for sure.   If you observe any of the warning signs or some other change in your skin, consult your physician immediately.

  An Open Sore that bleeds, oozes, or crusts and remains open for three or more weeks. A persistent, non-healing sore is a very common sign of an early basal cell carcinoma.   A Reddish Patch or irritated area, frequently occurring on the chest, shoulders, arms, or legs. Sometimes the patch crusts. It may also itch or hurt. At other times, it persists with no noticeable discomfort.   A Shiny Bump or nodule that is pearly or translucent and is often pink, red, or white. The bump can also be tan, black, or brown, especially in dark-haired people, and can be confused with a mole.   A Pink Growth with a slightly elevated rolled border and a crusted indentation in the center. As the growth slowly enlarges, tiny blood vessels may develop on the surface.   A Scar-like Area which is white, yellow or waxy, and often has poorly defined borders. The skin itself appears shiny and taut. This warning sign can indicate the presence of an aggressive tumor.