This case-sensitive code system http://smart.who.int/trust/CodeSystem/Domains-DEV defines the following codes:
Code
Display
Definition
DDCC
DDCC
The Digital Documentation for COVID-19 Certificates (DDCC) is defined by the SMART Implementation Guide at http://smart.who.int/ddcc
IPS-PILGRIMAGE
IPS for Pilgrimage
The IPS for Pilgrimage is defined by the SMART Implementation Guide at http://smart.who.int/ips-pilgrimage
PH4H
Pan-American Highway for Digital Health (PH4H)
The Pan-American Highway for Digital Health (PH4H) is defined by SMART Implementation Guide at https://worldhealthorganization.github.io/smart-ph4h/
ICVP
International Certificate of Vaccination of Prophylaxsis (ICVP)
The International Certificate of Vaccination of Prophylaxsis (ICVP) is defined by SMART Implementation Guide at https://worldhealthorganization.github.io/smart-icvp/