Umberto Eco quotes - page 10
The sign is usually considered as a correlation between a signifier and a signified (or between expression and content) and therefore as an action between pairs. Semiosis is, according to Peirce, "an action, or influence, which is, or involves, an operation of three subjects, such as a sign, its object, and its interpretant, this tri-relative influence not being in any way resolvable into an action between pairs".
Umberto Eco