[MargaretR]

In a book I have on old folklore is says that 'magpies are a bird of omen'
An old rhyme is used to interpret what sort of omen:-
"I saw 7 magpies in a tree
Six for you and one for me
One for sorrow, two for mirth
Three for a wedding and four for a birth
Five for silver, six for gold
Seven for a secret never to be told"

I suppose greeting a solitary magpie was to ward off the 'sorrow'