Speaker terminal polarity

I just unpacked my Cary 300B-SE mono blocks after being in storage for over 15 years.  Both speaker outputs (on each amp) look identical (not color coded) and neither is labeled + or -. I tried a continuity test against the amp chassis and both terminals read the same. How do I determine + from -?  Does it matter as long as I have each amp wired to its corresponding speaker the same way?

I must have asked this question when I got the amps 17 years ago, but can't locate the thread.  Standing by with red and black sharpie pens if necessary.