You're thinking of iodine as protective against nuclear radiation, such as gamma rays. Cell tower radiation and 5G are radio frequency, much longer wavelengths, not protected by iodine. Besides, salt contains only traces of iodine, not enough for gamma protection. They have iodine tablets for that.
It's actually an equilateral cross, with a loop on top for the chain. I wonder if she likes that people mistake it for an upside down cross.