My suggestion is adding a list of all the offences to the load screen, as by going through the watchlist it is fairly obvious that many of the first time offenders were simply unaware that certain actions were against the rules. I believe that if the offences are added to the load screen that there will be a reduction in the number of offenders, as many of them do not find out they are offending until they have received some sort of punishment.
Additionally, I feel that the definitions of certain offences need to be clarified, namely the offence of outside communication. With the current wording on the load screen, it implies to many players that communicating via chat channels or in real life is OK; this should be amended. Here is a replay of a person who believed communicating via xbox was OK.
evilgodzilla skyping and gamethrowing.SC2Replay
Here is a list of the offences I believe should be added to the load screen, and the wording which should be used for them so as to allow new players to clearly know what they can and cannot do:
Griefing:
Trolling or annoying people in such a way so as to probably reduce the chances of your own team achieving victory.
Game-Throwing:
Deliberately playing in a style which is counter to your own win condition. This includes revealing your own team members as mafia.
Outside Communication:
Communicating with players in the game using methods other than the chat in Mafia. This includes talking in real life.
Hacking (it may not seem immediately obvious as to why people need to be told this is an offence, but hacking one's bank files in other custom games goes largely unpunished, and as such I feel it needs to be stated to those who think Mafia is just another custom game):
Modifying one's bank files or using software to obtain an unfair advantage ingame.
Card-reading:
Asking a player to read all or parts of their role-card.
Abuse obviously does not need to be on the list.
Rolequitting:
Deliberately leaving the game shortly after receiving your role.
Many new players also see rules as hollow threats, and as such a statement such as:
'Offenders may be placed on the kick-vote or ban list'
would deter new players from offending.
I feel that this update to the load screen would both deter new players from offending, and also allow clean players to more easily identify and report offenders.
EDIT: I feel that this information would not be as effective if placed in the help screen for two reasons:
Firstly many players do not even click on the tabs in game, especially the new ones.
Secondly there is the current bug where the screens constantly scroll to the top, which would make it harder for players to read the rules under the help screen.
EDIT 2: It is also worth noting that I have divided the old 'Cheating' offence into two different offences, since the term 'Cheating' was too ambiguous.