The term 'crest' strictly does not refer to the shield or the coat of arms but to the crest on top of the shield which follows similar but slightly different lines of inheritance.
There is no official Appleby Coat of Arms. Coats of Arms belong to individuals and there may be none, one or more individual Applebys who have been granted Coats of Arms.
What is today generally accepted as the Appleby Coat of Arms and Family Crest was probably created during the Victorian era when discovering one's family history first became a fad. In the case of the Appleby Coat of Arms and Family Crest, it does accurately reflect the specific history and origins of Appleby-in-Westmorland and would have been created to reflect that history.
The leaves of the crest represents a location surrounded by forests; the helmet identifies the family's role in defence; the apple reflects the name's meaning.
Six marlett/swallows - this bird appears on the crests of many families of Irish descent. In Ireland the martlett was the bird of perpetual movement. Its appearance on a crest indicates one who has been dispossessed of their land, the number of birds could indicate the number of times this dispossession took place. In the case of an individual's coat of arms, six would indicate the person was the sixth son.
Dominant colour - Azure (blue) indicates strength and loyalty
Helmet - defence, defender
Vikings: Physical characteristics