At the very least it can be relayed to new members when they post a suggestion, so that they only make the mistake once. It's better that they mess up once and never again, as opposed to spamming up the board. Besides, I have an idea.
Perhaps when a user signs up, the PM that's sent out to their new account can have a list of links to posts they should read. The forum rules, of course, and some of the other things like the community-compiled list of mods, the modding resources, and some other useful things. Seeing as how the PM notification is at the very top of the board, new users are likely to see it.
Then the only problem would be if they deleted it without reading it. If they did that, they still have a chance of seeing the topic. If they don't see the topic, or choose to ignore it, then a user can reply with a link to the topic. If they ignore the link, then they're probably not very bright and they won't listen to us anyways.
Whatever happens, they'll see it.