I found this cool PDF at www.unixworks.net/papers/wp-007.pdf It talks about legal warning banners at the pre-login phase to SSH and consoles. It might be a good idea to provide yourself with a legal basis for action against intruders. These banners don't do much good against bots but if your experiencing a true cracker attempt, they could help with the legal aspect.
Anyway it's just a cool PDF I found. Just so you know I have a legal banner for both my SSH and console pre-login. You will find the PDF attached.