You can create a logout link using the Luminate Online Content Editor (WYSIWYG) editor in Luminate:
  1. Type out the text for the link
  2. Highlight the text
  3. Click Insert/Edit URL or Link Create Link  Insert/Edit URL icon
  4. Click Browse Links 
  5. Select User Registration
  6. Select Logout
  7. Click Select
  8. Click Insert

This is an example of the link created.
<a href="https://secure3.convio.net/xyz/site/UserLogin?logout=">Log Out</a>

NOTE: Your link will vary from the example - "XYZ" would be replaced with your organization's shortname and it may contain a different number (e.g. secure3).