I normally don't answer calls I don't recognize the number to, but if I might be expecting a call and have an inkling it might even possibly be spam, I just answer with a short 'ya?'

Slightly rude, but saying nothing at all is just bizarre to me.

Edit to add: One thing I've done for the last decade or so is use a number from an area code I don't live in. Most of my spam calls come from the same area code, so if I see that I know it's spam or a wrong number.