Soon after I'd finished my postgrad studies I took a job at Xmas at the local Royal Mail sorting office. It was my job to get a big bag of mail and fling each letter I picked out of it into one of a number of crates that were marked by postcodes. I suspect it works the same way in sorting offices across the globe - given zipcodes rather than postcodes, or whatever term is appropriate to each country.
Anyway. Anything that made a letter look 'official' rather than just 'friendly' got preferential treatment. Time and time again a supervisor would catch me on the point of chucking a letter into a crate, and check it - if there was anything - anything at all - that made said letter seem 'official'.
So, this year, on all the of the Xmas cards I've sent, down the left hand side of the envelope I've written NSU Ro80 4R 48/Z/gamma. It means absolutely nothing - I made it all up. But that's the point: it looks intimidating, exactly because it'll be meaningless to any post office worker. People are intimidated by incomprehensible series of letters and digits.
Try it. See if it helps. Report back here.
That is All.