Salam sis. I got my certificate from the Islamic society of my state which is Fl. there is one in philly Al-Aqsa 1501 Germantown Ave,
Philadelphia, PA 19122 as that is my home city ( south west ) and there are many masjids in the city. the certificate gives the date and the name of the 2 people there who heard your shahada. Then the Imam places his seal on it and signs it.