I know this question was raised before but I want to try to add some new details.

I think trust ratings should be visible on all boards for these reasons.

A) Most scammers promote their scam on their signature. Consequently any of their posts is potentially dangerous if their tag isn't visible.
B) Many scammers create threads and directly or indirectly promote their "business" under misleading topics on boards where trust ratings don't show up. On some local boards this is very frequent because there are less boards. Many scammers use translated ads to promote their scams on local boards.
C) Plagiarism is a form of exploration of other people's work for personal gain that deserves to be qualified as a scam that can be exploited on any board.
D) On the local boards, trust isn't active on many commercial/scam relevant boards:
On the English board trust is active in all alt coins boards, because they are easily promoted on any topics and are a typical scam domain. But on many local boards trust isn't active in alt coins boards. Example: Indonesian, German, French, Croatian, Korean, Italian, Portuguese, Greek, Turkish. It's active on the Indian or Polish.
Even the Spanish and Turkish Market boards, the Italian scam board or the German Project development don't have trust visible.
On the English board trust is active in the mining board, but not on many similar local boards: German, Indonesian, French, Romanian.

Just my two cents.