Single pieces found in archaeology are seldom taken as chessmen; they are much more likely to be general art objects. "Groups" of small objects are more likely chessmen if there are of more than two types. Many board games have used two kinds of pieces, but only chess uses six different kinds. A dig might not turn up all six forms, but more than two is indicative of chess. If the forms have characteristic chess figures (foot soldiers, kings, man on horse) this is even more convincing.