Question about earrings

Random question I had late at night. Would a police officer typically be allowed to wear earrings while on the job? I'm sure hoops or dangly earrings wouldn't be allowed because of the risk of them getting ripped out, but what about small flat-back studs or silicone sports studs that are clear and specifically designed to be next to impossible to catch on anything?

I'm sure different places have different rules, but I'd like to know what the rule is where you're at.