You're right, it's much easier in a marriage. But in public, you can't tell without looking like a sick pervert. "Excuse me m'am, are you in your period right now?" That's something I can't control and so I don't worry about it honestly. Because when you think about it, Israel didn't have public chairs or transit, etc.That sounds good for husband-wife situations... How about out in public? Do you try to find out if a chair has been sat in by a woman with a discharge?
If the answer is yes, or uncertain, is waiting until that evening good enough? Suppose one was in a society that rarely washed clothes, and bathed, like, one a week... Would waiting till the end of the week be OK? My impression from the law was to wash soon, make an effort to wash quickly...
In general, I try to wash regularly whenever I've been out in public, regardless of whether it's for bleeding issues.
And if I were live in a society that rarely washed clothes or bathed?
I think I'd find a different society.