Hello Robert,
As was already pointed out, not all religeous symbols and art are idols. Idols are worshiped as god(s), sacrifice offered to them etc etc...
I suppose that would depend entirely on their reasons for doing so. (He knows our hearts)
For I resolved to know nothing while I was with you except Jesus Christ, and him crucified.
Pax et Bonum
It is rather obvious that some have idolized the cross sir. I am sure we would agree it is a religious symbol. It is displayed on many houses of worship, and a large percentage of those who wear it as jewelry or have it or a fish attached to their cars would say they are making it known they are a Christian. In reality the cross has absolutely nothing to do with Christianity, but was figurative in pagan religions prior to Jesus coming to earth. So many pagan symbols of pagan gods infiltrate their way into "Christianity". There is religious aspects in many things sir, although unseen by most. When someone tries to idolize something other than God, or make any kind of symbol to represent Him, they are making a serious mistake.
Lets say Jesus actually did die on a cross, if that was your son and all his friends and even those who did not know him came around placing that symbol on their house or wearing it on their nect how would that make you feel, like they were disgusted at those who killed him, or showed their support to it. Heck I don't know, but I do know that a deer statue in your yard probably is not idolatry but a statue of buddah certainly would be. Any graven image that has religious significance is most likely not acceptable to God sir.