The model of the speech circuit proposed by Ferdinand de Saussure in "Course in General Linguistics" (1966 [1916]). A conversation is an exchange of vocalized mental signs. The drawing uses the oak clipart by rg1024 http://www.openclipart.org/detail/colored-oak-tree-by-rg1024
The diagram presents a visualization of intra-domain mapping in conceptual metonymy (as defined by George Lakoff and Mark Johnson in "Metaphors We Live By").
The model of the linguistic sign according to Ronald Langacker, as described in "Foundations of Cognitive Grammar" (1989). The sign is a pairing of a mental image of the concept and the mental image of the sound denoting this concept. The drawing uses the dog clipart by molumen http://www.openclipart.org/detail/13883