Bill Hicks had a great bit on this: www.youtube.com/watch?v=pJSZcxXe7IQ
I’m convinced it’s most often performative, consciously or otherwise, and a signal to make your ‘beliefs’ overt. Many seek to benefit from the perception of being associated with Christian beliefs, likely more than people who are truly living the prescriptions of their religious doctrine. I say this because Fox news hosts all have them and I can guarantee you none of those freaks are meaningfully sacrificing anything for those in need or performing works of good. I’m not advocating for this by the way, it’s a disservice to true believers to set a false pretense, and I’m one who believes actions speak louder than words. As far as I’m concerned wearing symbols and trinkets falls closer to the ‘words’ category of acts.