Well, I may be misunderstanding you, so I'll post both ways and hopefully that will cover your question. My vB4 installation is a little older, but it should still work the same.
To keep the SEO title in the URL you can use:
Code:
{vb:raw vboptions.bburl}/{vb:link forum, {vb:raw forum}}
e.g. https://www.vbulletin.com/forum/forumdisplay.php/
153-vBulletin-4-Questions-Problems-and-Troubleshooting
To REMOVE the SEO title, you can use:
Code:
{vb:raw vboptions.bburl}/forumdisplay.php/{vb:raw foruminfo.forumid}
e.g. https://www.vbulletin.com/forum/forumdisplay.php/
153
One of those should work for you, depending on what you were trying to achieve.