You may limit an ad to certain products by assigning them to the ad number in Ad Number Definition.
To associate products with an ad number:
After displaying the Ad Number Detail window in Ad Number Definition, click <Associated Products> to display a window showing all the product(s) for that client.
Select one or more products to which the ad will be limited by clicking the check box next to the product OR click the Select All icon 
to select all, then deselect one or more to be excluded.
Click <Save> to update and return to the Ad Number Detail window.