Martin (1992: 281-2):
The largest class [of exhausting processes] has to do with processes of signification. These can be grouped into three sets. One deals with the realisation relationships within semiotic systems; a second handles relationships between non-semiotic manifestations and their meanings; and the third has to do with meanings that are suggested rather than denoted:
[5:12] C-A-T spells cat.
[5:13] The red stands for the blood that's been shed.
[5:14] His behaviour smacked of jealousy.
By definition, the expression of a meaning, as when red betokens bloodshed, is semiotic. Semiotic means 'relating to signs' and signs are necessarily both content (signifié) and expression (signifiant).