[Jim S]

Not under Federation rules. Those little plastic bands are considered jewelry.
If they absolutely have to have them wear them taped to the body under the uniform, or in their jock.. they're washable.
Told that one to a kid that told me he promised his girlfriend that he'd always wear the chain and heart she gave him. I told him to put it in his jock becuase "how much closer to you can it get". He looked a second, broke into a big grin and said "YEAH!"