It's a double pole switch. If it's not having an internal light to indicate that the power is switched on, the side doesn't matter.
The one thing you should check is that the switch doesn't short the 2 wires with the mains voltage. If you misconnect it, this can happen.
The only good solution is measuring which wires have the mains, and checking the switch or measuring it as well to see which contacts are connected 2 each other once the switch is closed. If you don't have a meter, you can use a small test lamp that works on the main voltage for that purpose as well. Just be carefull as it's a high voltage you are working with. You don't want to short the mains and you don't want to touch it either.