Two very rare ploughshare tortoises at the Singapore Zoo had their shells engraved on Monday in a symbolic gesture against smuggling.
The process was done with a small portable drill that does not fully penetrate the shell, which has a thick layer of keratin, the same material that makes up fingernails.
"As long as you don't go too deep you won't hurt the tortoise," said Mr Richard Lewis, Madagascar programme director of the Durrell Wildlife Conservation Trust, which was involved in the ceremony.
The carved identification codes make the tortoises less desirable to smugglers and enable the authorities anywhere in the world to return them if they turn up in someone's suitcase. Monday's procedure was the first time engraving has been done in South-east Asia but tortoises in places such as the United States have been treated.
Ploughshare tortoises are found naturally only in north-western Madagascar and there are only about 400 adults left in the wild, although several institutions, including the Singapore Zoo, hold small populations to help prevent their extinction. Their beautiful shells make them a target for poachers, who sell them as exotic pets for tens of thousands of dollars.
In March, two smugglers were arrested with 52 of the tortoises while trying to enter Thailand. This was the largest seizure ever in South-east Asia.
The Singapore Zoo took in its two tortoises after the Agri-Food and Veterinary Authority confiscated them in an island-wide raid in 2009. The zoo believes they are about five years old.