In your campaign world maybe.Worth pointing out the issue with Knowledge checks and unfamiliar holy symbols is largely an issue because the same fairly small set of gods is generally worshipped across the entire campaign world-- so all the characters should always recognize all of them, as a matter of cultural immersion that all the players don't have.
In mine there's a pantheon for each non-Human race and a bunch for Humans, many of which have yet to enter play. Right now, for example, some of the PCs in my game have recently gone to a whole new (for the players as well) part of the world and are being exposed to cultures and peoples they'd never even heard of before.
In today's real world, yes. But 2500 years ago if a Greek devotee of Zeus or Artemis were to journey to the Far East the residents there 99.5% likely wouldn't have a clue what a Zeus or Artemis was, never mind what their holy symbols looked like (if they had any).Like maybe you need to make a Religion check to know what the Cross and the Crescent mean, but everyone knows who they belong to.