Yes, in the postbit/legacy (whichever you are using) template, replace:
<if condition="$post['signature']">
<!-- sig -->
<div>
__________________<br />
$post[signature]
</div>
<!-- / sig -->
</if>
with (replace XX with the forum ID you want to exclude)
<if condition="$post['signature'] AND $forum[forumid]!=X">
<!-- sig -->
<div>
__________________<br />
$post[signature]
</div>
<!-- / sig -->
</if>
Hope that helps.