R. Jannai said: I do not know what is this [Kabul]: whether we learnt of a slave's chain, but a wool hair-net is permitted; or perhaps we learnt of a wool hair-net and how much more so a slave's neckchain?
The word can mean both a hairnet and a slave’s chain. So what is a “slave’s chain”? Evidently a mark of his or her status worn in public.
But Samuel maintained: We learnt of a slave's neck-chain. Now, did Samuel say thus? Surely Samuel said: A slave may go out with a seal round his neck, but not with a seal on his garments?
What is the difference? The concern is that if this attachable mark or seal is pinned onto a garment, it may fall off. If it does, and the slave discovers this fact, he may take off his cloak and fold it over and carry it to hide that it is missing. This would constitute illegal carrying on Shabbat!
But not just slaves – it seems that these marks were also used by scholars to indicate their position, or perhaps their affiliation with a particular school. They (or at least one school was) were also forbidden to go out with a seal on their cloak.
Scholars and women and slaves. Interesting connections!