The Commens Dictionary
Quote from ‘Definitions for Baldwin's Dictionary [R]’
An icon is a representamen which refers to its object merely because it resembles, or is analogous to, that object. Such is a photograph, a figure in geometry, or an algebraical array of symbols which by virtue of the “rules,” or permissions to transform, […] are analogous to the objects they represent. An icon is so independent of its object, that it is immaterial whether the latter exists or not.