So both "stigmas" and "stigmata" are legitimate plural forms of "stigma." "Stigmas" is most often used when the figurative sense of disgrace is intended, while "stigmata" is most often used in its scientific senses and in reference to Jesus' wounds.

What is the singular form of stigmata?

stig·​ma | \ ˈstig-mə \ plural stigmas or stigmata\ stig-​ˈmä-​tə , ˈstig-​mə-​tə \

What does it mean if a person has stigmata?

People who have stigmata exhibit wounds that duplicate or represent those that Jesus is said to have endured during his crucifixion. The wounds typically appear on the stigmatic's hands and feet (as from crucifixion spikes) and also sometimes on the side (as from a spear) and hairline (as from a crown of thorns).