Search for "Nokia" in Qt 5 sources and you'll find a lot of occurences. Some of them are in the code, e.g.:

qtbase\examples\embedded\lightmaps\slippymap.cpp
qtbase\examples\embedded\styleexample\main.cpp
qtbase\examples\widgets\painting\basicdrawing\renderarea.cpp
qtbase\qmake\option.cpp

...others are in license headers, e.g.:

qtbase\qmake\generators\projectgenerator.cpp
qtbase\qmake\generators\projectgenerator.h
qtbase\src\dbus\qdbusxmlgenerator.cpp

I assume these should be changed to Qt Project or Digia, respectively.