Air Carrier Captain reported a Lithium Ion Battery package was loaded without providing a NOTOC to the flight crew during preflight. After further inspection it was determined that the specific UN code loaded is approved for transport without A NOTOC.

Narrative

During the pre-flight inspection; my First Officer (FO) noticed boxes with HAZMAT labels on them which said Lithium Ion batteries. After he informed me; I asked the Operations Agent about them and if there was a dangerous goods from for this flight. Operations Agent said there was not a dangerous goods from and that they were unaware of any issues with the cargo that was being loaded. The FO and I started to look through the FOM HAZMAT section to try and find more information about battery transports. He said the label on the boxes was similar to the one on page XX. These materials cannot be transported. I then called the Chief Pilot On Call for help. He looked into it and found that label marked are approved to be carried. I asked the FO if he remembered what number was on the label; but he was not able to specify since he didn't take a picture. I asked the Operations Agent again and they said they did not know how the boxes were labeled; but that they have been doing this for 35 years and never had a problem before with this cargo. I went to the Ramp Agent who was in charge and asked about the HAZMAT on board. He said there was not any HAZMAT on board. The problem was the cargo was piled behind 60 pieces of regular luggage; and they could not easily tell me what was on board. I had them move the bags so they could access the boxes. They found the label. These are approved for transport on Company aircraft and do not need a dangerous goods from. Notes - Our 35 year tenured Operations Agent was less than helpful about what specifically was on board. Her attitude struck me as; 'We do this every day. Why is there a problem.' Even though the Operations Agent was the one who climbed into the aft cargo hold and found one of the boxes and took a picture of the label to show me. The Ramp Agent who loaded the boxes didn't know what a HAZMAT sticker is obviously. There was not one piece of paper indicating the specifics of the items of cargo being loaded. And when I asked about all of this to our very senior Operations Agent; she responded with; 'Our station manager is worthless.' We finished the boarding process and left 20 minutes late.Suggestion - Even if a dangerous goods form is not required for specific HAZMAT; our Team Members should have available to them a detailed list of any cargo that has a HAZMAT sticker/label on it so we can verify that it is in fact approved for transport. Perhaps just a reference sheet. If not; our Pilots may find themselves concerned and unwilling to depart until the items are verified or removed. Our HAZMAT section is also poorly written especially when it come to determining if what is on board is one of the approved items. I think this should get some attention from the lead Operation folks.