Before he is to ship out he has to find his "masters mates and pilots license." That is the name of a maritime union. No such license exists. He also would not be in that union as that is only for ships' officers, which he obviously is not. He would have been in the "SIU" union, for deckhands. And he would need to supply his "AB" (able bodied seaman) ticket.
Near the start, Llewyn looks at the back of his album made with Mike Timlin. The biographical information below Mike, however, talks about Dave Van Ronk, the folk singer about whom the movie is loosely based.