Vayda,

I assume you mean around the neck. (Many religious brothers and sisters wear one on their belts.) It depends on the intent. This is not what a Rosary is intended for, so I can't recommend the practice. You would risk offending people.

If it's done respectfully out of piety and devotion, I suppose it might not be sinful (though, as I say, it is not really appropriate unless, it was the best place to store it, temporarily, while preparing to pray.)

Where you'd run into problems, is if it is done without proper reverence and respect, as if it were a common piece of jewelry, e.g., as a fashion statement (or, on the other end of the spectrum, as a magic talisman).

It's a Catholic devotional article, hence a symbol of Catholicism, and to use it in ways that were not intended devoid of its intended context, I think, would be disrespectful and hence sinful.

Eric