Can't place white sign

Hello !

This may be a stupid question but i can't figure why so i'll ask here.

Why can't i place my summon sign in some place in my game for exemple i'am able to place my sign in the DLC zone, kalameet, Ooacile Township etc.. but I want to help people in anor londo for S&O and i can't place my sign anywhere... nor in the undead parish for exemple for sen's fortress(Edit i jus had to go a little forward in sen to be able to put it so that's done), and this happening to me to a lot of other locations..

I can place my sign in the depth as well, and demon ruins, lost izalith.

Is there some kind of restricted area where to put you sign ?

Please enlighten me on the matter ^^

Edit 2 : I was rly stupid i can place my sign i was just in the wrong place each time and didn't not venture far enough in the zone..

There are certain areas in each zone that you can not place summon signs. These places are usually near zones , elevators , things of that nature.