The title might be something like "Read this now. Important information you need before posting or your pet hamster will be killed". Or something to that effect anyways. Make it a simple thing such as:

Please use the search function before creating a new thread to ensure it hasnt been discussed before. If it has, find the most relevant thread and ask your question there if it is not answered already. This reduces the amount of repeat threads and will save you from hearing how you needed to search in the first palce.

Maybe make it a message that automatically gets PM'ed to new people.

Put it someplace into the site agreement and then aska question on it before anybody can post the fist time to make sure they actually read it.

The thing is, most people who do post repeat questions/subjects without making at least a half-hearted attempt to search first, do so because they are lazy, or feel like they are so important that they don't need to. Adding another announcement won't change those attitudes, and won't help anything.

---jps

Have you seen how people drive?
Their lives can hang in the balance there.
Do you think people will read a suggestion here any more eagerly than they take a suggestion about their driving?