Yeah,
1. Login to your Admin Control Panel
2. Scroll down the left menu and find "Styles" (Click Modify)
3. Find the "PHP Parsed Code" section and add to it:
$usersig = bbcodeparse2($bbuserinfo[signature], "1", "1", "1", "1");
Now in the usercp template, instead of:
<td bgcolor="#F9F9F9"><normalfont>$bbuserinfo[signature]</td>
Use:
<td bgcolor="#F9F9F9"><normalfont>$usersig</td>

~
Hope that (works) helps