The observation, recognition and interpretation of signs of illness has been recognised as one of the cornerstones of medical practice since Hippocrates. Over the centuries, the repertoire of signifier terms used by medical writers has undergone numerous changes. This chapter traces the history of signifier terms used in English vernacular medicine from the Late Middle period to the Late Modern English period. Commenting on the frequencies of the individual terms as well as their many uses and changing meanings, this study demonstrates how a superficially generic lexical field can reflect changes in scientific thought style and index the individual authors’ intellectual and professional affiliations.