The words “Firm for the Union” were stamped on the coin, and Ms. Rojas stood her ground: her examination showed that it was genuine, and it stayed in the country. Like most other items seized at the post office, it was added to the collection of the National Museum.

Still, there is little incentive for unscrupulous traffickers to obey the law. A Sotheby’s auction of pre-Columbian works, held in Paris in March, took in more than $13 million for about 150 items. The auction occurred despite claims by the governments of Peru, Mexico, Guatemala and Costa Rica that many of the objects had been illegally removed from their countries.

And the penalties are relatively minor. Since 2007, no one has been sent to prison for cultural trafficking in Peru, and only five people have been given the maximum fine of about $1,900, at the current exchange rate, according to Blanca Alva, who is in charge of the Culture Ministry’s efforts to stop trafficking.

“Compare that to the prices that our pieces bring” in auctions abroad, Ms. Alva said.

Ms. Alva has also stepped up efforts to recover objects that made it out of the country, often many years ago. Last month, the Foreign Ministry announced the recovery of 125 pieces from the United States, Mexico, Switzerland and Chile, including pre-Columbian ceramic pieces, a 17th-century manuscript, colonial paintings and a silver receptacle for carrying the eucharist that was stolen from a church in Cuzco.

In 2011, Yale University began returning hundreds of artifacts carted away decades ago from Machu Picchu, the famous Incan citadel.

All of this taps into powerful notions of national pride and a lingering resentment over the colonial past. Such themes may have added resonance today in Peru, a country with a strong sense of its heritage, where a decade of sustained economic growth has ignited hopes for greater recognition and influence in the region and around the world.