Diabetic dermopathy (also known as shin spots) is a common skin condition frequently associated with diabetes. However, it is not specific to diabetes (i.e., it can occur in the general population).

Does it affect everyone with diabetes?
Upto 50% of individuals with diabetes are affected by the lesions. Age over 50 years and long-standing diabetes appear to be significant risk factors. Men are more commonly affected.Why it occurs?
Due to the thickening of small blood vessels (arterioles and capillaries) supplying the skin - they are called diabetic dermopathy.How does it look like?
Brownish or tanned spots on the shins (front of legs) in crops - also called Shin spots. They are initially red with an oval or circular shape, about 1 cm in diameter. Slowly, develop scaling and brown colour because of leakage of blood components into the superficial layers of skin. Finally, it fades in colour and shows indentation in the skin (due to atrophy).
Multiple hyperpigmented macules over both shins (shin spots) – Diabetic dermopathy

Also see : How does diabetes skin rash look like