Take a 1.5 volt battery and connect to the speaker wire momentarily and remove. Have someone else stationed at the speaker. When you apply 1.5v have the other person tell you if the woofer cone is moving out (towards you) or in (away from you). If moving towards you, then the + of the battery is the speaker positive. If it's moving away from you, it is the - of the speaker wire.

Some little satellite speakers have a capacitor on the input which will block the dc from the battery. You may see a slight movement, maybe not. Reverse the battery polarity in this case each time you tap the battery terminals and see if you see the cone move.