The Sound of Drums
The electric guitar amplifier seen in the Doctor's prologue has a plaque reading Magpie Electricals, a shop originally owned by Mr Magpie and visited by the Tenth Doctor and Rose Tyler in the episode "The Idiot's Lantern". The name often appears on electronic equipment throughout the series, such as Martha Jones' television in "The Sound of Drums", and a shop with the same name is seen in "The Beast Below".