A blue GPS icon in the upper right corner of your iPad or iPhone screen indicates that GPS location services are being used while the app is in the background.
Blue location services icon
This icon will only show if the Location Services setting for ForeFlight is set to While Using the App and a Track Log is being recorded in ForeFlight. Tapping on the icon will cause ForeFlight to open.
The Location Services setting is found in the iPad or iPhone Settings App under ForeFlight > Location. If this setting is set to Always or Never, this icon will not be seen.