Sulla the dictator became [in]famous for his proscription, giving the term a new -- and lethal -- meaning.
William Smith, D.C.L., LL.D.: A Dictionary of Greek and Roman Antiquities, John Murray, London, 1875. (Smith's Dictionary) adresses the subject best:
PROSCRIPTIO. The verb proscribere properly signifies to exhibit a thing for sale by means of a bill or advertisement: in this sense it occurs in a great many passages. But in the time of Sulla it assumed a very different meaning, for he applied it to a measure of his own invention (Vell. Pat. ii.28), namely, to the sale of the property of those who were put to death at his command, and who were themselves called proscripti. Read on
The only other systematic proscription happened 40 years later under the triumvirate of Gaius Julius Caesar (Octavianus), Marcus Antonius, and Marcus Aemilius Lepidus. Newer scholarship disputes the number of their victims listed in the above article.