The combinatorics of i -boxes has recently been introduced by Kashiwara, Kim, Oh and Park in the study of cluster algebras arising from the representation theory of quantum affine algebras.In this article, we associate to each chain of i -boxes a signed word, which canonically determines a cluster seed, following Berenstein, Fomin and Zelevinsky.By bridging these two different languages, we are able to provide a quick solution to the problem of explicitly determining the exchange matrices associ