Society of the Priests of Saint Sulpice

The Society of Priests of Saint-Sulpice (French: Compagnie des Prêtres de Saint-Sulpice; PSS), also known as the Sulpicians, is a society of apostolic life of pontifical right for men, named after the Church of Saint-Sulpice, Paris, where it was founded. Members add the postnominal letters PSS. Typically, the society's priests become full members only after ordination and some years of pastoral work.

Source: Wikipedia — Society of the Priests of Saint Sulpice (CC BY-SA 4.0)