I still can't really figure out what this thing is. The back of it says "souvenir" so I am guessing it was a locally produced memento, possibly all printed. The imperfect signature of Lindburgh hmay have been the only sample the producer could find.
It might also be that the photo and signature were the printed parts and the rest was written by someone. The last line seems to identify the person who witnessed the events. (This is my ultimate theory.)
In any case, it is a remembrance of his visit to Brussels, Belgium after landing in Paris.
As you had mentioned, the L and G end unnaturally. They seem cut off, which supports the idea that it is a preprint.
Without seeing it in hand there is no way to be sure, but the smudge could be a live ink smudge from when the notations were written that was coincidentally placed on the signature.