My grandmother's sedula
Someone doing his family history came across some pre-war documents and asked me what CN meant, which he found on a document identifying his great-grandfather, with a series of numbers following the CN. Without seeing the document, I suggested that it meant "Cédula Number."
Cédula is a Spanish word. Originally it meant a royal order or law. In time, it was used as a tax document and eventually a personal identification document (the cédula de identidad).
Even under the early American Naval Government, the term cédula was kept. Every adult had to have one. It made sense. The people of Guam had no passports; few had drivers licenses. The sedula (Chamorro spelling) was the only document of identification most people had.