Preventing Visitors from Activating Replacement Variables 
In many cases you will want to prevent your users from being able to activate replacement variables by posting trigger text in their messages.

For this reason, it is recommended that you set any replacement variables that should be used in templates only to appear as HTML tags, such as <myreplacement>.

This is done because most forums do not allow visitors to post raw HTML in their messages (this is seen as a serious security risk). In forums where HTML posting is disallowed, any special HTML characters such as the < and > characters are replaced with their equivalent HTML character entities to prevent the HTML code from being interpreted as HTML rather than printed text.

For example, the < character is replaced with &lt; and the > character is replaced with &gt;. This replacing of special HTML characters makes it impossible for a user to post <myreplacement> in their messages, as it would be translated into &lt;myreplacement&gt;, which does not match the trigger text. It will therefore not be replaced with the replacement text for your <myreplacement> variable.
User Contributed Notes: Preventing Visitors from Activating Replacement Variables