A pentegram is a symbol commonly used in wicca
below are a few pictures:
A pentagram is the shape of a five-pointed star drawn with five straight strokes.
No.Yes and No. (This all happens in Book 3 of the Mortal Instruments City of Glass.) The reason of yes is because Valentine impaled the Mortal Sword straight into Jace's heart. This all happened in Lake Lyn. Valentine summoned the Angel Raziel, the angel who created Shadowhunters, when Jace was dead. Clary was there when all of this happened and put a rune on the shore of Lake Lyn that meant, Mene mene tekel upharsin, the same one rune that she used to destroy Valentine's ship. This she used so that the pentegram that was around the angel didn't work. The reason for no is because the angel killed Valentine and gave one favor to Clary, as he did thousand of years ago with Jonathan Shadowhunter. Clary asked the angel to bring back Jace and he came safe and still alive.
No. A subliminal message by definition can not be perceived. In order to convey a visual message subliminally you must present it for a time period below the absolute threshold for vision which is roughly 50 milliseconds. The bible, being a book, has no way of doing that.