In this paper I am advocating a structuralist theory of mental representation. For a structuralist theory of mental representation to be defended satisfactorily, the naturalistic and causal constraints have to be satisfied first. The more intractable of the two, i.e., the naturalistic constraint, indicates that to account for the mental representation, we should not invoke "a full-blown interpreting mind". So, the aim of the paper is to show how the naturalistic and causal constraints could be satisfied. It aims to offer a strategy for grounding the structure of the mental representations in nature. The strategy that I offer is inspired by Marcello Barbieri's code model of biosemiotics.