Needless to say that, in all accounts, I've always wished I had a panoramic image/photo of the locations, to use as reflections for my 3d environment.
These markers indicate spots where the user can take a street view from.
They indicate the perspective of the structure/object on the screen.
While the StreetView Grabber dialog is still open, select the URL of the Google street view and press Ctrl+C to copy it.
Click OK to close the dialog and see the reflection bitmap in the Viewport.