A.US immigration officials were fond of using abbreviations and numbers. Some of these notations referred to events that happened on Ellis Island. For example, if you see S.I. by your ancestor’s name, that means he was held for the Board of Special Inquiry on the island. You might also see stamped next to his name the word admitted or deported—indicating what the board decided about his fate. Either one means you should check the end of the passenger list for detained aliens and Board of Special Inquiry pages, which will give you more information on that passenger.
Other abbreviations reference actions that happened after the immigrant landed—for example, if your great-grandfather applied for naturalization, a government and official may have checked and made a note on the passenger record to verify the immigrant’s arrival.
Notations had different meanings depending on the column in which these cryptic entries were made. To understand the notations on your ancestor’s arrival list, see Marian L. Smith’s article “Interpreting US Immigration Manifest Annotations,” online at http://www2.jewishgen.org/InfoFiles/Manifests. It originally was published in the Spring 1996 issue of Avotaynu: The International Review of Jewish Genealogy.