Calling spirits in with hidden sigils?

Quick question here. If I were to hang a spirit sigil up to invite and allow the spirit into my home, in your opinions would it need displayed out in the open? I want to do this using a sigil hidden perhaps inside a picture (something with a multi-layer frame and hide it between the cardboard and the backing). Then i think I’ll hang it on a wall in the hallway. It should be nice and inconspicuous. No one will think a thing of it. But will it work hidden like that?

Yes, there is no need to keep the sigil visible. I have to hide mine where I am currently living, still works.

Oh I work with them often and then return them to their hiding place stored in my bedroom. I just bring them out to charge and use them as needed. What I am planning though now is to keep one open and changed, hidden behind a simple harmless looking picture in a high traffic area of my house. Basically I want to turn this picture into a portal for a chosen spirit and his familiars to work inside my apartment.

Yeah I am pretty much trying to do something that many people would say never do, not only inviting demons in, but giving them an open door. I’ve considered how someone might warn against it, but I have my specific reasons for this kind of working.

Also while on this subject, is there perhaps a better way then actually using the sigil? Or anything else I can add to the hidden “gateway?”