Oh yes, duh, I automatically assumed that what he meant by collar is what I would mean by collar.

You should ask him what he means by "collared". Maybe for him it's just something akin to "going steady" (like wearing his ring meant back in the fifties), where he is claiming you as his and not available for someone else, not asking you to say you'll be with him forever. If that's all it is, it might be more appropriate for you to wear it.