In general, you can wear minimal jewellery. Common-sense is a factor, it’s about what is appropriate for a Police Officer and for safety.
For example, you can wear wedding and other significant rings, but not too many. Body piercings that are not visible when in uniform are okay, but you will need to think seriously about the risk of injury before wearing these on duty.
Bracelets, chains, or necklaces are not permitted when in uniform for obvious safety reasons. Medic-alert bracelets are allowed.