Light. Leaking.

Light leaking has been a persistent problem with Unity 5 / Enlighten since the beginning. I am surprised this issue has not been resolved more convincingly at this point. That being said, I have encountered workarounds including light blockers, UV pack margins, lighting resolution, etc.

Can we please put an end to this, or until then, can someone please provide a clear implementation strategy to avoid this altogether?

I have attached a screenshot illustrating the problem

For most of the time selecting option in mesh render for specific object: “cast shadow - double side” work for me.
But I have that problem only with decals/sings on walls and it always work, but hard to tell if it will work the same way for this scene.