Sometime you see an aircraft flying oddly and wonder. Allow me to recommend an ADS-B app, this is the iOS app OpenADSB:
This one was tracking CA-56. I wonder why?
Anyway, an ADS-B app shows all sorts of interesting stuff. Some time ago it showed FLIR surveilling San Diego:
Anyway, go grab yourself an app, there are others too, and hit the ‘show trails’ button to see where an aircraft has been. Sometimes its quite interesting.