For balance, I've never witnessed this stuff, or heard of such goings on in any facility I've used.
And I've never seen warning signs.
I don't think it's rife across the nation.
I don't doubt your experience.
(Or lack of, in this case)
But flashing , and other intimidating behaviour by men, of both a sexual, and non sexual nature is a common enough hazard for women.
So there's clearly far more than just one or two blokes doing it 'for kicks'
Small wonder really that many women want to reserve what few 'safe spaces' they
do have for themselves .
If that kind of behaviour was an almost vanishingly small rarity, then there wouldn't be a problem with sharing spaces in the first place.
I don't think it's the sight of a willy that offends most females in the first place.
It's the potential hazards associated with its owner, that bothers most .