Slaves used to have different חותמות they would were as indications they were slaves. It is not real carrying on Shabbos but the rabbis were concerned about the slave taking it off to conceal that he was a slave. This concern applies to emblems made by the save himself, but an emblem made by his master can be worn bc the slave would be too scared to ever take if out out of disrespect.

Even the emblems made by the master may only be worn on the slaves neck, but those attached to the garment are forbidden. We’re concerned the emblem may fall off and the slave, scared of his master seeing the garment without the emblem, may come to fold it over and wrap it on his shoulders which is carrying on Shabbos.

Metal emblems are always forbidden bc if they become detached the slave may be compelled to carry them back for the owner. The permit is only for clay ones.

No emblems are considered כלים and so they are not susceptible to tumah. They don’t “decorate” the slave.

Sometimes slaves went out with bells on them. Those are certainly כלים because they “adorn” the slave and could become tamei. Slave can’t go out on Shabbos with one on the neck bc if it became detached he may carry it back. One sewn into his garment is ok.

Animals only sometimes went out with bells. Plain animal bells cannot become tamei bc animals aren’t adorned. If the bells have clapper in them and make noise, they do accept tumah, bc making noise is a significant function for humans.

Bells on doors do not accept tumah bc they are battel to the door which has not tumah as its part of the ground.

Bells for animals or children are only tamei if they have the clapper in them. If they became tamei with the clapper and that the clapper is removed, the tumah still remains bc the bell could still make noise by banging against a pot.