Unable to assume a fair form, Sauron's hand was blackened after the death of his body in the Fall of Númenor. After Isildur cut his ring-finger off with the shards of his father's sword, Sauron's one hand had four remaining fingers.
Portrayal in adaptations
In Peter Jackson's Lord of the Rings film trilogy, Isildur is shown to cut off several of Sauron's fingers, as opposed to one. Sauron is not shown or referenced to have regained a physical form afterwards.