The blackboard of the middle ages
A brightly colored ink that hardens the skin.
A small, ordinary looking red pouch that deters all but the most skilled thieves.
This thick sauce, usually a condiment on the platters of the rich, has found a niche in the equipment of thieves.
Draw the party together as debtors to the local lord, king, head of the thieves guild, or mercenary clan, who is forcing them to work together to pay off their debts.