Cross as fashion accessory is quite common, and it really not exclusive to Christianity anyway.
The crucifix with the Body of Christ is ALWAYS more than a fashion statement, even when worn sacrilegiously, like one might suppose that Madonna might be doing in the picture on the page with the article. I associate her more with the Black Mass crowd than with Catholicism.
Positive or negative, the crucifix is just too powerful of an image for it to express nothing but fashion.
When I see a stranger wearing a crucifix or on the dashboard of the car, I presume the stranger is a Catholic, just as much as when I see the pope himself with that crucifix.
Crosses are not inherently religious symbols. The crucifix is inherently Christian. As such, people using the crucifix outside of a religious context are few and far between.