According to Prof. Tim Crane, one of the elements that links "religious impulse" and "identification" - the two essential characteristics of religion, according to him overlooked by new atheists - is the sacred. The notion of sacred forms one of the key elements of the characteristics of religion, any religion. He said that anything could be sacred... a person, a thing, a text, an object... anything! But this means that there is a distinction between the sacred and the profane.
The sacred in so far as it represents the 'transcendence' aspect and is a point of unification among the people who agree upon its being distinct from other things, especially profane things, serves as a connecting factor. So from what I understand, a thing to be sacred has to fulfill both these criterion: represent transcendence and be a source of unity. That broadly gives us a vague criterion of judging something as sacred or not. So there could be something that actually reflects the transcendence but not noticed or accepted by us OR something that is socially projected but not actually sharing in the transcendence aspect of reality. Neither of these can be called sacred(?)
But there is one thing he mentioned in passing: "...the sacred need not be the supernatural."
That set me thinking. Then I remembered the whole distinction between the sign and the symbol, especially made by Paul Ricoeur. Am not sure if that fits in with Prof. Tim Crane's understanding of the sacred. However, I don't think Paul Ricoeur would have serious objections to the sacred not being the supernatural. In as much as what is considered sacred shares the 'immanent' aspect with us human beings while being the representation of the 'transcendent', that what eludes material quantification, the sacred does not become the supernatural. And if it does turn supernatural, then it loses its immanent character. I'm thinking of all that we consider 'sacred' within the Catholic tradition: relics, the altar, consecrated statues, churches... all are basically still natural objects or things. Even the person of Mother Mary, as long as she was here on earth she was a human being, immanent; but now we treat her as supernatural, but she is no more with us in that immanent form as she once did. (The only exception I can think of is the Holy Communion. Can it be classified under this: representing the sacred but not the sacred itself?)
On the other hand, there is this dilemma as to whether we need this distinction of sacred and profane at all. After all, if we are true to our Christian tradition, there is nothing that is 'not sacred'. Everything, however mundane it appears, is sacred. So perhaps we can at the most speak of 'degrees of sacredness', in so far as it is ascribed to a thing by us collectively and not merely in itself being a representation of the 'trascendence'.