Board Thread:Dark Souls/@comment-11227880-20130726041341/@comment-25257440-20160603091433

Yes, it's possible to put a summon sign in front of a fog wall. You can check where you can put the summon sign yourself by having the Soapstone item selected and walking around with it. When the icon for the Soapstone goes dark, you cannot put a sumon sign at that spot.