From CyberWurx Customer Wiki

Understanding the MOTD

The MOTD or Message Of The Day is a text file inside the base game directory of your server. It is the first things gamers see when they connect to your server. Post Orange Box gameservers have the capability to point to a single HTML file.

Pre-Orange Box Games

You can use basic HTML in this MOTD as well as plaintext.

Welcome to my server! Have a good time.

Respect the admins!

Post-Orange Box Games

You can simply put a link to a website that will show up as your MOTD.

http://mywebsite.com/motd.html