"Blue Peter" in naval signalling is the flag which represents "P". It is formed of a white square or rectangle on a blue background. As blue is the predominant colour, and Peter was the early phonetic word for "P" (It's now "Papa"), the flag is popularly known as the "Blue Peter". As well as forming part of longer signals, it is traditionally hoisted to indicate that a ship is about to depart from port, and is also used as the preparatory flag when starting a yacht race.

One assumes that, as an informative childrens' programme, "Blue Peter" aimed to prepare the little darlings for life. (Grieving dead dogs and avoiding pools of elephant piss are skills that are bound to come in useful one day!).