turing machines – Mathematical Symbol

I remember about 10+ years ago there was a mathematical symbol used to represent population sustainability.

It resembled a downward or upward angled arrow but in dot form…if remember it was represented in a 4×4 grid but maybe have been larger. It is the result of population seed eventuality, with no additional variances introduced into the initial population. The result was an infinite sustainable population model that was based on reproduction and death of neighbor’s

Any help refreshing my aged memory, would be most welcomed.

Had to pick a tag, so please correct the tags if not representative to the question.