Criminality is a status gained when you commit a crime or so. Here is a list of the things you should avoid doing in STWALT if you don't want to end up as a brigand:

Criminal Actions
Action How to Do Action Bounty Other Effects
Stealing an Apple Steal from an Apple Tree 50 Gold N/A
Stealing a Rope Steal from a Well 50 Gold N/A
Desecrating a Gygax shrine Steal items from a shrine 75 Gold Possible curse for 100 days
Begging at Castle/Village Get caught begging N/A Immediate escort to jail
Stealing a Book Steal from the Royal Library N/A Immediate escort to jail
Looting a corpse Steal from a corpse 100 Gold N/A
Stealing from a Caravan Look for goodies in an attacked caravan ? N/A
Robbery Rob a peasant, stranger, hermit, merchant, or princess ? N/A

-Robbing your fellow peasants, adventurers, strangers, hermits, merchants and the cute princess you are encountering ( this happens when they recognize your face).

You are informed when you shamefully became a brigand by the announcement "You're wanted by the law!"

If you are a criminal, the hobbit shire, dwarven fortress, elf village and merchant guild will not do business with you except if you are wearing a mask.

The criminal status will disappear by hiring a hobbit lawyer at the hobbit shire for 250 golds, by serving time in prison or by an amnesty in X days. 

Finishing a quest without doing any crime will earn you the respect of being a paladin. (Tip: If a paladin commits crime, he will not gain xp until he is forgiven)