Luckily for the zorua, no. That is to say, the easiest method is to look closely at someone for any signs of zorua-like features. Maybe it’s red-tipped black hair (that naturally grows that way) or bright red fingers and toes. Maybe their ears or teeth are pointed, or maybe they forgot to disguise their tails. Or maybe they act a little fox-like (running on all fours, eating or drinking by plunging their faces in a dish, or so forth).
However, just because a method is easy doesn’t make it reliable. Experienced or well-trained zorua, especially those on the brink of evolution, are often much better at disguising themselves than younger zorua, and thus, they’re nearly impossible to detect unless you have a pokémon capable of seeing through illusions (such as those with Foresight) or a device specially made for such a purpose.
(Don’t worry, anonymous. Your secret should be safe.)