Stolen property

Because if ownership is established after the fact, you forfeit the goods.

that’s the case with cars for instance, but how realistic is it with stuff in your living room? Do I need to worry about everything I bought on craigslist?

Out of curiosity: does goodwill verify that donations were not stolen goods?

If you own them, take an electric engraving tool and carve your SIN (Canada) or SSN (US) on the plate that carries the speaker outlets on the back of the speaker. 

When buying speakers ask whether there are any marks like that on them, and decline to buy them if there are, and tell the seller that if they show up and do have previously undisclosed identifying marks you will seek redress.

This whole thread is ridiculous. The OP won't even give any details, so it's all a bunch of hypothetical nonsense.

Receiving stolen property is a crime. And failing to undertake sufficient due diligence can result in prosecution and conviction.  Failing to do due diligence also incentivises criminals to continue to steal and fence stolen goods.

I agree with Roxy. The OP has written only ten words and is totally unengaging or the least bit thankful for all of your advice. Move on from this one.