Found this old pic of the counter area inside Portland airport circa 1971. Not Northwest Orient (Western Airlines I believe) but gives us the flavor and look of the times.
Enjoy 
Thank you, David! I am researching for fiction and wanted to know what the interior of the airport looked like. I'm not within range of Portland to go researching their public archives that aren't on the Internet. Some other online sleuths had also wondered about the height of the counters. While I doubt Cooper would have filled in his own ticket, this does show adequate space for a passenger to write something. Some airline counters in other airports did not have enough space and the ticket agents were seated lower. Any further photos of the interior of the Portland airport (or Portland in general) in that era would be much appreciated.
I was too young in 1971, but I'm sure some airlines might be different..it always seems to be off record when things like this occur? we have a ticket agent that worked for NW state the passengers didn't fill out the tickets in any way.."the FBI told me this, or that" doesn't fly with me...Cooper would of known a copy is left behind...
I straight-up don't think someone that fussy about collecting the matchbook and notes would leave a handwriting sample behind for no very good reason. As for the notes sent later to newspapers - one was handwritten, but in a way that suggests to me the writer was using his non-dominant hand. That's a slightly educated guess based on years of correcting papers, a left-handed best friend, and an ambidextrous dad; a proper handwriting analyst could tell you. I go back and forth on whether the letters were written by Cooper, but they link to each other in ways that suggest they could have been written by the same person travelling almost straight up and down the west coast between Vancouver BC and Sacramento.
Whether letter 5 was written by Cooper or not, though, I think it's a good assumption he'd have wiped the area for fingerprints. I liked a previous poster's out-of-box idea he might have used the tie to do it, though honestly there would have been like a hundred napkins on that plane - and what analysis has been done on the towel that was found?
Of course, they can't even be 100% sure the tie is Cooper's. I assume it is simply because the case attracted so much publicity, even passengers who de-planed before Cooper boarded would have taken some notice of the case. I think anyone would have stepped up and said, "Sorry, that's my tie, my wife gave it to me and I always hated it and thought I'd ditch it. Who knew? My bad." Again, conjecture. You learn in life it's hard enough to understand your own thought processes or actions 100%, let alone anyone else's.
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