Criminal status can be seen in how some mobs react to you.  In particular,
some will shout that there's a criminal and attack you on the spot.

Becoming a criminal is easy!  PKing is a direct route.  Having terrible
karma is a slower way to being a criminal.

Criminal status can be removed by being killed by the elite guards Talmar
or Madraelthon.  Bad karma cannot.

See Also: PK, Karma