From Forum Nokia Wiki

Operator Logo is an image that displays on the upper most part of the main screen of the phone which corresponds to the Network Provider. It can be changed with our own created logo.

Stpes:

• Create one .bmp image with 97 x 25 pixels.
• Save it with the format of MCC_MNC_0.bmp (MCC=Mobile Country Code and MNC= Mobile Network Code)
• Use it in the .pkg file like:

"C:\MyNewLogo\404_57_0.bmp"-"!:\system\apps\phone\404_57_0.bmp"

NOTE: In the above example: 404 = India ( Country Code) and 57 = CellOne ( Network Operator Code)