they use the symbolism BECAUSE they believe the symbols themselves have magical power. It is a sort of spell that they believe they are casting.
They do not stop at only flashing symbols. There are violent actions that often precede or go along side such spells
It's about demon control and demon favor. So using symbolism shows their intent not only toward you but also to others and it shows you who these evil POS's are.
So don't use the gun analogy because it doesn't fit.