The Bavli, Shabas 62 amud 1, as explained by Rashi, continues a long discussion regarding what objects are considered clothing (or adornments), so may be worn outside (an eruv) on Shabas, and what objects are not clothing/adornment, so may not be worn outside on Shabas:
It quotes the mishna as saying that a signet ring cannot be worn by a woman, but a non-signet ring can. (I'm writing here about divinely imposed prohibitions. As a practical matter, and even as discussed in the text there, there are rabbinically imposed prohibitions in some of these cases. So please don't take any of what I write here as practical permission; consult your rabbi with any practical questions.)
Ula then notes that the reverse is true for a man: a signet ring can be worn by a man, but not a non-signet ring.
Rav Yosef notes that Ula seems to hold that whatever is considered clothing/adornment for one person is not necessarily clothing/adornment for another (as, otherwise, any ring permitted for women or men would be permitted for everyone). He attempts to refute this position from a piece of Tosefta that says that anyone can go out wearing sack because shepherds do (implying that what's clothing/adornment for shepherds is permitted for anyone).
- Rav Yosef answers his own question: Ula indeed holds that what's permitted for one is permitted for all — but not between the sexes, as "women are a nation unto themselves".
The g'mara then asks why a woman's wearing a signet ring outside should be forbidden. After all, the prohibition is carrying — but she's carrying it on her finger, which is an unusual part of the body for carrying things with. The action should be permitted for that reason (כלאחר יד).
- Rabi Yirm'ya answers that treasuresses frequently carry around signet rings on their fingers. Thus, that method of carrying a signet ring is considered usual.
Okay, so treasuresses usually carry around signet rings on their fingers — that is, they wear them. So why doesn't the logic of the shepherds' sack apply to the treasuresses' rings? Recall that anyone can wear sack because shepherds wear sack. So why can't any woman wear a signet ring because treasuresses wear signet rings?