Usage: MARK <nick> <reason>
The MARK command is used to mark a nick name with a reason why it was marked, this is useful if a user has been abusive and an operator wants to make a note of the offense. Other operators encountering the nick name may then check the properties of the nick and will see the previous problem(s) with that user.
/mark Thomas Seen flooding and cloning.
See also PROP NICK MARKED.