I have an 'adults only' section on my forum where occasionally topics are discussed that are not allowed with Ad Sense, so I use a simple conditional to not show the ad in that specific forum.
Assuming you have some forums where you meet Google Ad Sense terms and a few where you don't you can get away with a conditional- but bottom line if you run a warez site or something they aren't going to allow you to have adsense anywhere.
My conditional is:
Code:
<if condition="THIS_SCRIPT != 'adv_index' AND THIS_SCRIPT != 'register' AND $GLOBALS[forumid] != 6">
AD CODE HERE
</if>
My adult forum is id 6... I also I don't show ads on register.php and my vb advanced homepage which are the other two parts of the conditional.
For more info you can see an article on conditionals in the VB 3.8 articles section.