I have several crew list mentions for a relative who was working on ships coming in at the Port of New York (found on the Ellis Island site) around the 1920s. Most of the lists have a number next to each of the crew member's names. One of the lists includes the heading "Seaman's Certificate No." and the numbers are listed below this heading. I have already determined that my relative's number was the same on every list, and therefore had some meaning. Until I saw the seaman's certificate number listing I did not know if it was a passport number or something else. Is this certificate number the same sort of item that you are discussing, and if so, where do I find the records for it? I should also mention if the number is similar to what you are discussing, perhaps the person who is looking for their relative's number might find it written near their relative's name on a manifest of a ship's crew. Passenger arrivals should be indexed and searchable for that time frame. You can check these at the National Archives or rent them from a Family History Center. There is no letter in the number my relative had, simply numbers. Do I assume it is a "Z" number? (In other words, did they also have X, W, P, etc. numbers?) Debbie