Iconicity has been defined in three majors ways in the sign language literature. Some authors describe iconicity as a similarity mapping between a signifier (the mental representation of the form side of a linguistic sign) and its referent, while others state that iconicity is to be understood as a similarity mapping between a signifier and its meaning. Other scholars have defined iconicity as a similarity mapping between a signifier and some other mental representation. The goal of this paper is to give an overview of the consequences entailed by defining iconicity as a mapping between a signifier and its referent, a signifier and its meaning, or a signifier and some mental concept. These consequences will be discussed from different theoretical perspectives. It will be argued that definitions viewing iconicity as a mapping between a signifier and some associated mental concept work best, while definitions based on reference and meaning run into several theoretical problems or are, at least, rather theory specific.