From the opb report it sounds like they were essentially just little badges that say "police".
There is no federal "police" department. There's a number of federal agencies that do "law" enforcement and similar, but none of them are police. US Police departments are a part of incorporated cities. Outside of such cities, you get sheriffs. Between states you get the FBI, Treasury, Marshalls, etc.
These people were being taken to a federal courthouse, implying that they were federal agents, the only groups in Portland at the moment are ICE and the US Marshall service. The former has a fairly terrible human and constitutional rights record so I would guess it was probably them, but who knows - we know that they've had people "arrested" but have no record of the arrest. Which means it was an abduction by the federal gov with the intent to terrorise and escalate the conflict.