when I was younger I had an urban fantasy universe where religious symbols repelled vampires on a “faith of the weilder” basis; but also, it was a magic universe where magic sigils and circles and amulets were how you channel ambient magic in the universe to focus and direct it and do what you want, and religious symbols operated in a similar manner. Faith was required to actually give the religious symbol any power to repel vampires, but also, the more distinct and intricate the symbol was, the better it was able to concentrate and direct that faith power. A Star of David is good, and a hamsa is great; a crucifix works well but a plain cross is useless.