there are a lot of papers on this (some made by inducing seizures in people under lab conditions). The most seizure causing things you could display are simply bars or a grid with moving details, sizes, or alternating in colors.
Basically if it gives you a headache to stare at or just has this sucky attention grabbing feel to it when you look at it its likely to cause seizures. I CBA to dig up the papers on this but there are a bunch if you want to really get into this.
However as the above study iirc doesn't directly state that these patterns cause discomfort and doesn't contain any examples I suggest reading chapter 10 "Photosensitive Epilepsy and Visual Discomfort" of "hierarchies in neurology (1989)" on page 70-71 which proposes this AND contains an example you can look at yourself.
