The McGuffin of the 1942 Movie 'Casablanca'

A McGuffin is "an object, event, or character in a story that lacks intrinsic importance but serves to set and keep the plot in motion."

Here is question: What is the McGuffin in the movie?

Many have seen the 1942 movie, "Casablanca" one time or more. But how many viewers have actually seen the two 'letters of transiit' (i.e. the McGuffin.) These no question asked 'letters of transit' metioned many times in the movie, but never seen. The war resistance couple Victor Laszlo (Henreid) and Ilsa Lund (Bergman) acquired them from Rick Blaine (Bogart)to escape French-Morocco from the clutches of the Nazi.

What is this McGuffin looks like?   Here it is.

So long. We'll always have Paris.