hi there thank you for using HCM The black dot on toenail is not a definitive sign for diabetes, so u should not be scared of it. It can appear due to multiple causes like sometimes because of trauma, sometimes it occurs due to bacterial or fungal infection, or in a very small percentage it can be a reason for skin cancer. But since for the ist time u hve noticed, if it has not change its size or colour or there are no visible changes on your toe nail you do not need to be worried as it seems to be harmless. if u think it to b a complication of diabetes and feel anxious,the best advice I can give you is to get a test of your blood sugar fasting. if result is normal, stay relaxed and enjoy your life. hope this answer is helpful. kind regards