This is a question that recently cropped up. Can we apply the spell Magic Vestment to the Ring of Force Shield?
There was argument about if it actually counts as a shield, since it says "can be wielded by the wearer as if it were a heavy shield (+2 AC)." The closest we found was this quote by Joshua Frost "Ring of force shield essentially grants you a +2 shield bonus to your AC as if you were wielding a heavy shield without needing to actually wield anything. It requires no hands to wield--just an open ring slot." From this thread (http://paizo.com/threads/rzs2jq8b?Potions#14).
I'm leaning towards no, but we couldn't find a conclusive answer.
i would allow it to be cast on the force shield itself while it is activated as the spell can be used on shields. but it goes off and not return if deactivated.
"It can be activated and deactivated at will as a free action."
No. The ring is not a shield. It generates a spell effect (wall of force) which is also not a shield. It is thus untargetable by the Magic Vestment spell.
That it gives a shield bonus to AC is not relevant. [Otherwise, you could apply it to Bracers of Armor.]
/cevah