This was happening in Portland.
Apparently, they were allowed to conceal their name tags, because there was some concern that individual officers were, or would be, doxxed. That is, they worried that exposing their names would allow people to track down their places of residence, their families, etc.
The police chief apparently allowed them to cover the name tags, and instead write their city employee numbers over the top. Theoretically, this would allow officers to be identified for the purpose of complaints and other accountability issues, without directly revealing their identities to the public at large.
I still think it’s bullshit, but if it worked properly and if the officers put the correct number on their uniform, they could at least still be identified and held accountable for any inappropriate use of force.