Air Carrier Maintenance Lead Technician reported identifying Hazmat cargo labeled 'forbidden for transport aboard passenger aircraft' at destination arrival. Reporter suggested more Ramp personnel training is required.

Narrative

As we were offloading mail out of the fwd cargo I noticed some boxes that had Lithium-Ion battery UN3481 labels and also a white label that said 'LITHIUM ION BATTERIES- FORBIDDEN FOR TRANSPORT ABOARD PASSENGER AIRCRAFT' There were at least 20 boxes that I could see. Some were individual boxes and some were within the white mesh like bags that USPS uses. [I identified] while offloading the mail. I saw many boxes with the Dangerous Goods label on them.This event occurred because the crew Chief and crew loading Aircraft X on [date] did nothing to stop this mail. I can see that the crew Chief who scanned the bags on this flight was [name]. I do not know if he was also in the fwd cargo area or if he had another crew load the mail. I told a Customer Service Manager. He asked for no information. Mail went to the cargo facility to be given to the USPS. More training and knowledge of why this is so important for all of us to be aware of these hazards. With Lithium-Ion batteries becoming more and more popular I think this should be a reoccurring lesson in person class.