Teeth

Scholars have had several secret symbols over the years, but none as enduring as (disembodied) teeth. Scholars will draw a tooth on important shipments and letters, pack a tooth into crates that have been searched, or present each other with teeth to show that they are part of the organization.
The symbol began as a password between closed bases. Scholars in trouble and needing entrance to a base might be missing all sorts of items, seals, et cetera, but they would be almost guaranteed to still have enough teeth in their head to be able to tear one out and present it to an ally. Exchanging your own severed teeth also wasn't so common among outsiders that it was a useless code; if someone reacted with confusion or shock at the tooth gift, it probably meant that they weren't part of the organization and couldn't be trusted. People that were often in danger outside of their home domain were (and are) known to carry pliers as a macabre joke about the situation.
In the modern era, there are so many Scholars that it's common to be working with someone you don't recognize. If everyone was pulling teeth out at every meeting, they'd run out of teeth to pull. A drawing of a tooth continues to be used in mail, but in person, people often plan ahead and exchange some sort of animal tooth. Shark teeth are common, mostly because there are so many pieces of shark tooth jewelry to be easily purchased. If it's not an emergency situation, most people will accept "Hey, okay, I lost my necklace earlier, please don't make me pull out my teeth for this" as an acceptable identifier.
Because the tooth became a signal before Classical Mages of the Third Age split from Scholars, and because of the long history of double or triple agents between the two groups, teeth function as a secret sign to both Classical Mages and Scholars. Tooth pulling cannot weed out one group from another, and both groups have been working for years to try to find a new signal that isn't something they have in common with their enemies.

Item type

Religious / Ritualistic

Manufacturer

The Alliance of the Wandering Scholars