As a counter-point to the prior example of the rook, Go stones are interesting because they illustrate the semiotic concept of codes. A code is essentially a framework needed to make sense of a sign; you are able to read and understand this sentence because you know the relevant code - English.
Unlike the rook, Go stones only operate as rules-signs: there is simply no fictional element here. While we could interpret the rook on its own as representing a tower, a Go stone does not represent anything.
However, if we know the relevant code - the rules of Go - the stone is a sign, as it signifies the rules of how it works, or the game of Go in general. As someone who knows the code, I cannot look at a Go stone and think of it as anything but.
Of course, these stones can also carry an enormous cultural meaning as well, you just have to know the codes.
