In several of his papers, Charles S. Peirce illustrates processes of interpreting and understanding signs by examples from second language vocabulary teaching and learning. The insights conveyed by means of these little pedagogical scenarios are not meant as contributions to the psychology of second language learning, but they aim at elucidating fundamental semiotic implications of knowledge acquisition in general. Peirce's semiotic premise that a well-understood sign is one that represents an object and creates an interpretant is essential to the understanding of how new words and signs in general can be taught and learned. The article argues that Peirce's theory of the object of the sign, especially of the necessity of collateral experience of the object of a sign, can help to understand the riddle posed by of the Meno paradox of the impossibility of learning what we do not yet know. It examines the semiotic implications of the didactic methods of teaching and learning through translation, ostension, mental and real images, as well as metacognition, and it shows how icons, indices, and symbols are essential to learning new words.