I think that what defines a symbol as “religious” would be the intention. Many symbols are common across cultures and and not intended as anything except geometric or good-looking decorations. It becomes religious when the creator or wearer intends for it to be a representation of their faith. So, interlocking triangles are not “Jewish” unless they are intended to be that way. I woudl say that a Jewish person might well buy one and use it as a symbol of their faith, in which case it would become religious.
When I created this thread I was thinking about whether the craftsmen who made the tsuba were deliberately creating tosogu with religious symbols for people to declare their faith, or as talismans etc. I do like the way the thread has evolved though… It is nice to see such a wide-ranging discussion.