Stupid question

Ha! We're still here. At least I am. Maybe you've all been replaced by duplicates...
I switched the red and black on my secondary stereo, a Marantz CD63SE, a Pioneer receiver, some old Infinity SM speakers, and some Monster cable. I played Beck's Sea Change. I couldn't tell the difference between black to black and black to red.
Not particularly conclusive, but if I had heard a difference in this system I would have assumed it would be even more apparent in my main system.
I was not able to switch the polarity on my bass amp; the speaker is connected by a plug.
I'm afraid my guitar amps' speaker connectors are too fragile to mess with.
So until I have the patience to try this on my main rig I remain convinced the "polarity" of this AC signal makes no difference.

AC signal? I thought we were talking about speaker cables. At least I was.

Thanks for following up.
I am too lazy to do the test ;)

Yes, I meant AC in the general sense of the signal in the speaker cable having positive and negative voltages, not in the sense of a power cable. This was my point initially, that since the signal in the speaker wires is AC, revolving around zero volts, that it doesn't matter which way it's plugged in red-to-black and black-to-red or red-to-red and black-to-black.
Sorry, I don't think I'm describing this well. And full disclosure: my degree was in electrical engineering, so I ought to be able to be clearer. Like most engineers, I need to draw a diagram to explain my point, which doesn't work well on a forum like this.
I have a long weekend coming up. I'll see if I can repeat the experiment on my better system then. I've only put this off because my Audio Magic speaker wires are thick and unwieldy and my binding posts are so close together on my speakers that I have to be careful red doesn't touch black. (I'm not skeptical about the impact of zero impedance!)