[Bartweiss]

Three big causes:

First, home bathrooms are reliably single-user. Some people are deeply uncomfortable with the idea of sharing a bathroom with people of another gender (though exactly which people they would not want to share with is a complicated question). Interestingly, this seems to be a bigger deal in the US, where our stalls are shoddy and easy to see into.

Second, cleanliness. Mostly, home bathrooms stay clean on a system of "if you make a mess you'll get yelled at". That's not viable in public settings, so gendering helps ensure that there are clean toilet seats for those who need to sit on them. Again, not totally effective, but relevant.

Third, most public and business bathrooms have a bunch of gendered additions which aren't present in homes. Urinals, hygiene/contraceptive vending, and (controversially) changing tables are the big ones.

For a sanity check on that list, think about the public bathrooms that aren't gendered. Single-person bathrooms are often marked male/female/family/disabled, on the grounds that they have a toilet, changing tables, and cause no particular gender issues. Similarly, porta-potties are usually unisex, whether or not they include a urinal. Again, they're single-user and generally filthy no matter who uses them.

So there's a bunch of reasons. But the third - the most objective - doesn't actually require gendered signage. A "facilities" list would be more useful and effective for those issues. The second is a bit ambiguous - gender doesn't seem to be the strongest predictor of bathroom hygiene, and there are options here. The first is the strictly gendered one, but it's actually quite complex! For all the concern of "gender identity doesn't make a person look like they fit here", "gender assigned at birth" is no better at ensuring "only people who look like they belong here". The ways to achieve that would be subjective and probably inconsistent between complainants.

Reasons for signage, then, but not necessarily for gendered signage.

[edblarney]

"gender doesn't seem to be the strongest predictor of bathroom hygiene"

It definitely is when you have very few elements to chose from.

When the 'men's' one-ey is 'in use' in Starbucks, I often go into the 'women's' - and it's very consistently cleaner.

It is what it is.

[tptacek]

So you're saying we should have binary signed toilets so that you can ignore the signs?

[euyyn]

> Urinals, hygiene/contraceptive vending, and (controversially) changing tables are the big ones.

I think I've seen baby-changing tables at all if not most male restrooms at Google.

Urinals... I've never seen another person's trunk when using urinals. I'd get upset if you tried to look at mine no matter your sex or gender. And I'd get as upset as a woman if you showed it like an exhibicionist, even though I have one too. So I think in practice, at Google, urinals wouldn't ultimately matter.

Hygiene and contraceptive vending I can see how people might want to be more private about.