'Sinthom' is Lacan's neologism for a 'constellation' of signifiers that circulate around an empty center. There is no 'objective' basis for meaning in the case of a sinthom, but, like the psychological 'symptom' of the individual, the sinthom supports a structural relationship among subjects, and between subjects and the object world they support through belief, action, and knowledge.
Sinthoms are common, particularly where the perceiving subject must invest heavily in some object or source of authority. The king is a king, says Pascal, because his subjects believe he is. Take away that belief, and the king has no power - indeed, he has no identity as a king. Pascal went further to show how the metonymical practice of religion was more effective than real belief, because it created around the subject a context of belief that was more reliable and effective than sheer belief would be. 'Kneel and pray,' Pascal advised. 'The rest will come later.'
'Going through the motions' may sound cynical, but most relationships, such as the famous Hegelian master-servant relationship, which permeates social relationships and structures, is based on just such actions. The participants may express cynical attitudes, claim that they are 'just going through the motions,' but in effect they are subscribing to the symbolic network effectively.
Artists use sinthoms in the form of repeated motifs that effectively guide audience attention to 'empty centers of meaning' that resist interpretation but serve important, indeed crucial, structural roles. An example would be Hitchcock's use of tracking shots to focus on some (metonymic) detail that transforms the meaning of a scene, as in the long tracking shot in 'Notorious' that ends by framing the key Alicia has stolen that will open up the secrets of her Nazi-husband's wine cellar.
Picasso's development of sinthoms, in combination with various anamorphic tricks, is notable. In 'Les Desmoiselles d'Avignon,' a figure on the left holds a curtain back to reveal the space of representation, an iconistic reference par excellence. With the same flair for planting puzzles from literature, the figure on the right signals the theme of Melancholia, who was always shown seated, with elbow on knee and hand on chin. The figure at the rear looks in on the 'room' from a cosmic perspective. The 'curtain' is really the blue sky, admitting a 4th-dimensional element akin to the audience's own intrusive sagittal line. Entrance and exit to the 'embodiment' of representation duplicates the cosmos described by Macrobius, where souls enter and exit through the same 'layers' of planetary influences. In birth, the soul acquires qualities from each planet; in death the pattern must be narrated in reverse, like a palindrome, to effect a successful cleansing and final rest.
Sinthoms are different from symbols because of their 'open-ended' meaning. Instead of determinate archtypes, sinthoms involve the act of interpretation, including ignorance and misinterpretation along with the 'enactment of meaning' guided by a structure that insures direct, rather than indirect, realization.