Nothing special about < in a database, just go ahead and treat it as any other char.
When you go to display it as html, however, things are different: this is the lead-in character for html tags, so naturally it's not going to display. Instead, you have to use the "html entity" for that graphic, which is &lt;.
It may be enough in some cases to just write a literal &lt; in your code. If you need to process a whole string, use htmlspecialchars(), which converts only less-than, greater-than, ampersand, and double-quote, or htmlentities(), which converts all chars that have defined html entity codes.
