The Hand of Trax is a bronze replica of the hand of a thief, severed at the wrist, bone and muscle modeled in metal. Curses are written into the 'skin' of the hand, warming the metal with the slight magical resonance it creates.
|This picture is from the BBC or something (and was probably actually a healing votive, but that's a topic for another time)|
Some scholars speculate that Trax was an ancient god of justice, with many swords of different sizes, each bearing the crime it punishes written on its blade. Others suggest Trax was a god of Criminals, his many swords keys that can cleave open any defence.
Either way, when a hand of Trax is created, it is modeled after an executed thief to punish them even in death with eternally burning hands, that they will never forget their crime.
Thieves will then steal the Hand to gain the powers of the Thief that came before them.
There are many ways to benefit from having a Hand of Trax; you might drown it in water, to soothe the pain of the criminal's spirit and thus gain their blessing. You could wet it with your own blood and so steal the memories of the thief's muscles, your hands dancing to the unconscious tunes of master criminals.
Either way, the best way to benefit from a hand is to have it be stolen from you, which superstition decrees to be good luck in all thiefly matters. Thieves are very superstitious.
The most famous Hand of Trax was modeled after a particularly infamous master-thief, and when it was inevitably stolen its new owner cut off their own hand, and used their ill-gotten-gains as a prosthetic. With this they performed many miraculous feats, until the hand was torn from their arm in a back-alley duel. Sometimes, the Hands become more famous than the people who benefit from them.