power cord directionality

When we talk about A.C. power or POWER Cords, there is no Physical science that specifies "polarity"

Polarity on A.C. power is mainly for safety. In the off position the device can be safely serviced because there is zero power after the power switch. This is why the HOT side of the cord is directly connected to the power switch. 
As for a device not equip with a power switch be careful.

U.L (underwriter labratories) is the largest testing facility in the U.S. tasked with safety testing things like power cords. I would venture to say that in this era, inorder to get the U.L. listing a device not equip with a power switch would require a polarizes power cord.

A picture is worth a thousand words. The signal travels in two directions 🔛 as it alternates at whatever frequency applies, as someone said. But you only care about the signal when it travels in the direction of the speakers. You can forget about the signal whenever it’s traveling in the opposite direction 🔙 because it doesn’t affect sound quality. The only signal that affects SQ is the one that is traveling toward the speakers. 🔜

danvignau

... transformers are DC to keep from blasting everything with a 60 cps hum ...

Sorry, but you don’t know what you’re talking about. A transformer will not pass pure DC. A transformer can’t work with DC - its primary coil would have a static, constant magnetic field, so it would not induce EMF on the secondary coil.

... Current for a 400 cps signal, for example, goes back and forth 400 times per second. It does not flow like water.

Correct.

The current driven magnetic force pushs the speaker out 400 times a second and pulls it in 400 times per second ...

No, it doesn’t. You’ve just described an 800 hZ (or cps, or cycles per second) signal. A cycle includes both halves of the AC waveform.

Directional wiring for alternating currents, such as for fuses, speaker, and interconnect wires, is pure witchcraft, i.e. fantasy.

That’s not necessarily so. As Geoff pointed out, with a speaker cable, we really only care about the direction of the signal when it flows towards the speaker.

A better question would be: Are cable direction differences audible?

Sorry, I thought the topic on this thread was related to "power cords"

not to be confused with "signal"

In a perfect world you should never hear power or its side effects.

You want the signal to be clean.