The "arrow convention" was started by Bruce Brisson when he developed the "shotgun" interconnect while at Monstercable (he left to start MIT cables.)
Cable manufacturers now put arrows on everything! However the arrows were originally meant only for single ended shotgun type interconnects, and have nothing to do with "signal flow." The arrows always point to the end of the (single ended shotgun) interconnect where the shield and the negative signal conductor are soldered together to the ground 'ring' of the RCA plug. The other end of the shield is not connected to the RCA plug (it 'floats'.)**
I think the business about "signal flow" was concocted so technologically challenged audio salesmen could explain cable installation to their customers ;--)) It's too bad this nonsense got started, when it would have been just as easy to say "All arrows should point to the preamp." This would have insured proper star-grounding, with the preamp at the center of the star, and avoided the resulting (and common) mistake of installing the preamp-to-amp cables backwards.
Arrows on all other kinds of cables -- XLR, speaker, power, and data -- are utterly meaningless from an electrical standpoint, since audio signals (and wall voltage) are alternating current and interact with conductors the same way in either direction.
** If you want to check, and have a single-ended interconnect with removable connector barrels (and arrows ;--) you can slide the barrels back and you will see that only he arrowhead end has the shield soldered to the RCA connector. At the other end, the shield has been trimmed short, and usually covered with a piece of tape or shrinkwrap.
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