Ring, common
These simple looking rings are used by merchants to alert them of potential manipulation. Whenever a spell of the illusion or enchantment school is cast within 15 feet of the ring, it vibrates slightly. It provides no other information about the spell (caster, school, level, etc).
Nice!
Neat
This is a useful if basic magic item
Great for negotiations with disagreeable spellcasters
I love utility magic item ! Yours is nice and make a lot a sense from a worldbuilding perspective. Maybe rather to have the ring being simple looking to be conceivable I will do the opposite. Making an obvious ring with the mark of the mearchant guild or something like that. To signify that they are not to be taken for fool.