Does a varistor have anode or cathode or polarity?
The best source is the datasheet. 

However metal-oxide-varistors are symmetric by construction. Typically a layer of zinc-oxide is sandwiched between two metal plates. There is no polarity.

So you can mount MOVs in any direction.

Other kinds of TVS, such as unipolar TVS diodes do have polarity, and it is typically indicated with a ring, like normal diodes.