You could make something up like: Simulations as we know them have limitations. Given those limitations, things like recursion require more processing power than simulating a bouncy ball. And if we can detect slowdowns, or a higher state of energy simply by going between two mirrors, we could count it as evidence towards a simulated existence.
Of course this is all conjecture, and assumes that there is no effort to conceal the facts, but at least it is a solid, actionable starting point.
Of course this is all conjecture, and assumes that there is no effort to conceal the facts, but at least it is a solid, actionable starting point.