An unblinking sign of Graves' Disease
Stellwag's sign is one of the classic ophtalmological signs in thyroid opthalmopathy associated with a chronic high level of thyroid hormones. It is named after the Austrian ophthalmologist Carl Stellwag von Carion and describes infrequent blinking associated with Dalrymple's Sign: retraction of the upper eyelids producing apparent widening of the palpebral opening.
With other words, you're looking at somebody with big, protruding eyes who rarely blinks. How scary is that?
Onset can be rapid over just a couple of days to gradual, taking years to decades for the eyes to protrude.