Why does some ice trays have a + on one end and a - on the other?

Question

Why does some ice trays have a + on one end and a - on the other?

Answer 1

so you know how to stack them to get the best ice cube. plus on negative (or negative on plus). it's designed so the top doesn't sink into the bottom tray.

when you store the trays dry, they fit together and don't take up as much room. when you make ice, you have to store them oppostite ( + on -) or the top will sink into the bottom tray and you'll get a big frozen mess.