Joser !
What equipment have you got connected to your Viera TV ?
Have you got a Sky HD+ Box ?
It is possible that your TV Set is not switching over to Sky HD automatically and you will have to go into TV Menu to choose appropriate external connection.
I haven't got Panasonic myself therefore go through the On-Screen Menu and try to find a link whereby your set can be programmed to switch over Automatically to HDMI when viewing HD Programmes. It seems to me that the logo appears because you have not switched set over view HD.