I agree; but more convincing than your two examples (since they'd be recognized as familiar religious symbols, albeit from other belief systems) is the way Nick reacted to the obsidian knife in "Blackwing", since the episode doesn't suggest he's familiar with its religious role. It suggests that other people's beliefs can imbue a symbol with power to hurt vampires.

That is a much better example, for the reason you stated. Blackwing is not an episode I've watched very often. I'll have to take a look at the scene.