I used to get SSSS all the time. Much of my travel is short notice, very often my itinerary changes in the middle of a trip. I have purchased walk up tickets from various points in North America to LHR, NRT and FRA, as well as other points in North America simply because my schedule has changed.

I found that once I hit Platinum on DL my SSSS stopped showing up on DL walk up tickets. This happened with US as well when I hit Gold. I think it is because this type of travel is common on my FF account history.

Oddly enough I once did a walk up from JFK to KWI, with approximately four hours on the ground at KWI to photograph a quick assignment, and I had no SSSS and I was never questioned by the ticket agent or any US or Kuwaiti officials about my itinerary......I expected that one to set off alarm bells.