Despite knowing the wire colors inside USB cables need not follow any particular convention, this still came as a surprise:
Yes, that’s a negative indicator on the meter: it reads -5.020 V.
No, I didn’t swap the test probe banana plugs on the other end.
A bit of continuity testing shows the green and white data wires are also reversed, so whoever assembled the cable simply soldered the proper wire color sequence backwards onto both connectors. As long as you don’t cut the cable to reuse the connectors, it’s all good.
Memo to Self: Stop trusting, always verify!
The Smell of Molten Projects in the Morning 
I would market this as “tamper resistant” ..