An alternative to placing site guidelines on a welcome page or in the navigation header (where I believe they would eventually be glossed over) would be to link to the guidelines from within inappropriate comments. If a comment gets downmodded below a certain level, it could either be appended with a link to the site guidelines or altogether replaced by a link to the guidelines. This would probably be a better hint to the commenter that something he/she said may have violated the guidelines. This may also have the side effect of keeping people from abusing the downmod option.

This could be one approach to dealing with the "broken windows" issue: https://qht.co/item?id=373356