Folks of the Guild
Anyone can steal things. That doesn't make them a Thief. That title goes only to the Folk of The Guild.
None in The Guild wear Medium or Heavy Armour except occasionally as a disguise. The same goes for wielding shields. One should not lower oneself to the stature of a mere Fighting-Man.
For each job a Thief has pulled off (i.e. for each level in the class, including the first) they can be inducted into a single trade. This requires connecting with a local Guild cell. This is easy enough in all but the smallest settlements.
Training requires spending a work-week with a mentor. Offering a gift to your trainer, monetary or otherwise, is customary but not required (a fifth of any recent winnings is a good amount). Offering respect is required.
Training concludes at the end of the week when the Thief gains the adornment relevant to that trade, which they must always display henceforth. Each adornment is an ironic reference to a punishment doled out by the law.
Your collection of adornments signals your specialisations to other Folks while also subtly boasting that you haven't yet been caught and maimed by some law-man. It's fine to bear a Mark of the Law instead of the relevant adornment: it just means you're a worse Thief.
The Trades
The Barbers
Automatically hit and double any damage when attacking an unaware opponent from behind.
Barbers wear scarves or cravats, a dainty reminder of both their trade - a slit throat - and the murderer's sentence - a hangman's noose. Neck adornments play a special part in Guild symbolism as one of the Two Ends: in this case, Death by the Law.
The Scriveners
5-in-6 chance of reading non-magical text in any language. Failures can be re-attempted after gaining another level.
Scriveners wear a piercing on the tip of their tongue to show they haven't had theirs cut off or split yet. A silver or gold tongue prosthetic can also suffice.
The Woodturners
Can cast spells from scrolls as if a Magic-User of one's Thief level. 1-in-6 chance of mis-casting.
Woodturners are marked with a curved facial scar, small and subtle but undeniably there. It is a reference to the Crescent Brand: the official punishment on Udore's City Coast for stealing from a Magi.
The Plasterers
Can climb sheer surfaces of up to 100' without fail. Each subsequent stretch incurs a 1-in-6 chance of falling.
Plasterers wear a pair of matching bangles or bracelets, a reminder that they've dodged the pillory for now.
The Locksmiths
4-in-6 chance of opening locks if appropriately equipped. Failures can be re-attempted after gaining another level.
A Locksmiths must wear at least five rings. This is to highlight that they still possess all their fingers.
The Butchers
4-in-6 chance of detecting or removing a trap. When removing traps, a result of 5 indicates failure while a result of 6 indicates triggering the trap.
Butchers bear a flower on their person just as the deceased bear one on their grave. The flower is the icon of the second and more noble of the Two Ends: Death on the Job.
The Tailors
4-in-6 chance of picking a pocket. A result of 5 indicates failure while a result of 6 indicates detection.
Tailors keep a stick of chalk or a pencil behind their ear. This adornment is a reference to the marking of the neck or face with a tattoo, as criminals caught in the Nine Valley Kingdoms are.
The Farriers
5-in-6 chance of passing through an occupied room without detection.
Farriers, named so after the "clop-clop" of a horse's hooves, wear piercings on their nose to show they haven't had theirs removed.
The Thatchers
5-in-6 chance of hearing subtle noises or making out whispered conversation.
Thatchers ("always dropping from the eaves") wear piercings on their Good Ear to show that it hasn't been notched or cut off.
The Chandlers
Always evade detection while motionless in shadow.
A chandler goes barefoot or wears only sandals or foot-wraps. This is to display that they retain all ten toes.
These Trades replace the special abilities of the B/X Thief. Levelling rate and other statistical gains (Hit Die, THAC0, Saving Throws) are unaltered.
This is part of an ongoing series of reworked B/X classes, inspired by Idraluna's Chromatic Mages and Wealth is What You See. The intention is to embody practitioners of each of the Classes in the Hypo-Diegetic world.