Statistically, assuming that the probability of consecutive Ziggy’s referring to the axiom was independent, one would need a run of 14 axiom-free Ziggy’s to be able to assert with 95% confidence that the likelihood a given strip referring to the axiom was < 20%.
I’d test it, but the thought of examining 14 consecutive Ziggy’s gives me the heebie-jeebies.
Furthermore, I’m not sure I’d be able to determine whether a partciular strip refers to the axiom or not. I don’t understand the axiom, and even if I did, great art is ambiguous and subject to multiple interpretation and can refer to a lot of things. So can Ziggy. I mean, if Ziggy’s goldfish threatens to eat him, has he not selected Ziggy from a set?