Merrill (and DEShaw before that) enforced it by forcing us to provide duplicate trade confirmations to the compliance department for all accounts held by people living at the same address. That’s fairly common in finance.
My current employer does not, so you’d only run into trouble if FINRA detected unusual profits and flagged it to the company securities counsel or the SEC made an inquiry.
My perspective is “if your company tells you they don’t want you to short shares or trade in options in the company, don’t try to find ‘one clever hack’ around the policy.”
The only exception I’d make is if you have a complete financial freedom amount of equity built up, at which point, I’d consider quitting the company, and only then entering into such a hedging transaction outside of a blackout window (and when you had no material, non-public information). That would likely pass any “valid purpose” tests and be considered clean by regulators. (It’s not really the company I’d worry about; they can only fire you and whistleblow on you. It’s the regulators that I’d worry about. The company policy is designed to protect them, but also help keep you out of the grey areas as well.)
Also see 12-15 in section III here: https://www.finra.org/rules-guidance/notices/19-18
There is a lot of automated review (post-trade) to find and flag possibly suspicious activity. I think the FINRA team spoke at one of the Re:invent sessions (maybe even in a keynote?) about how they detect possibly anomalous trades for manual review.