Since I was never stopped, I can only assume that it was a result of a
traffic camera at an intersection.
What's unusual was that it was only a warning. In this day-and-age of
using traffic fines to fill public coffers, I was surprised.
I've never heard of a traffic camera system that looked for expired
windshield stickers, so I really doubt that's what happened. I'd also
be surprised if a camera ticket arrived just 2 days after the
incident. Probably a cop saw your 11 sticker and wrote down your
license plate.
Jimmy