This essay studied the acting theories of Diderot, Delsarte, Meyerhold, and Artaud to know the historical formation of 'sign acting' and its theoretical and aesthetic appropriateness. The sign acting so far discussed shows the repetitive patterns of idea as follows. The sign acting (1) emphasizes the physical expression such as gesture and movement, (2) assumes that the physical expression functions as a sign evoking special emotion and thought, (3) thus recommends the imitation of the outer sign, (4) uses a tableau for the effective reception of outer sign, (5) aims for the spectator oriented aesthetics as it stresses the result of outer sign rather than the creative process of a role, (6) assumes that the emotional reaction or the intellectual understanding springs from the physical experience, (7) thus emphasizes the physical language rather than speech, (8) can attain the appropriateness of physical language by the recent theories of cognitive science. Besides having such commonness, the sign acting also reveals the individual differences. For instance, the intended sign for Diderot and Delsarte was the sign of emotion, for Meyerhold the stylized sign of circus and acrobatics, and for Artaud the spiritual sign. If Diderot and Meyerhold demands the cool consciousness for the correct sign acting, Artaud's sign acting tends to pursue the state of trance. And if Diderot, Delsarte, and Meyerhold think the sign acting on the level of sensory appeal, Artaud insists that the sign acting should dismantle the spectator's sense. As such the discussion of sign acting shows both recurrent ideas and new visions, forming an unity out of diversity. Perhaps the sign acting is a matter of practice before we consider it as a theory. It is not only supposed to have been existed practically since ancient theatre, but also used by actors consciously and unconsciously in expressing certain emotion and thought. We need to study the sign acting more academically, considering its long history and aesthetic potentials. In fact the sign acting has been an essential element of acting, in spite of bad reputation judging it as a banal and worn-out style. It is true that the sign acting, in the worst case, could produce a stereotypical expression. It was this aspect of sign acting that caused a fierce negative reaction of the realists who sought the natural expression based upon psychological truth. Of course the sign acting has a serious problem when it stays banal and artificial. But we need to see this issue from a different perspective. What is the natural expression of emotion? How is it free from the learned way of expression? In some respect, we use, in reality, a learned expression of emotion that could be accepted socially. For instance, when we attend a funeral, we use the outer sign of mourning gestures learned socially. If a semiotic expression pervades various aspects of our life, the acting, being the representation of life, seems not to be free from codified expression. The sign acting could be used consciously and unconsciously in all kinds of acting.