Some simple Xs and Os, noughts and crosses, tic tac toe…

You could even mix the X and O blocks around to simulate an actual game of tic tac toe.

These blocks would be a great opportunity to play with transparency – imagine those centre squares (on point) in a colour that blends the two crossover colours. The blocks could be made using rectangles, squares, and a few triangles of background fabric to fill out the block.