Every page of a TYPO3 site has this in the HTML source code:

<!-- 
    This website is powered by TYPO3 - inspiring people
    to share! TYPO3 is a free open source Content
    Management Framework initially created by Kasper 
    Skaarhoj and licensed under GNU/GPL. TYPO3 is 
    copyright 1998-2006 of Kasper Skaarhoj. 
    Extensions are copyright of their respective owners.
    Information and contribution at 
    http:// typo3.com/ and http:// typo3.org/
-->

If you are a commercial TYPO3 developer, this is a great place to put your name, contact info, and level of participation on every project you work on. You never know when someone who is ready to start a TYPO3 website project may be looking at the source code in one of your sites.

Try this TypoScript code in the setup of your site template:

config.headerComment (
    ===============================
    Site design and TYPO3 integration by Your Info
    ===============================
)

Now, clear the cache, look at the front end and view the source code. You will see your message appear above the general "This website is powered by TYPO3..."

Look at the HTML source code on this Busy Noggin page for a real life example of the results of this code.