A martlet is a heraldic charge depicting a stylized bird with short tufts of feathers in the place of legs. Swifts, formerly also called martlets, have such small legs that they were believed to have none at all.
The inability of the martlet to land is often seen to symbolize the constant quest for knowledge and learning.
It has been suggested that this same restlessness is the reason for the use of the martlet in English heraldry as the cadency mark of the fourth son: the first son inherited the estate, the second and third traditionally went into the Church and the Army, and the fourth had no well-defined place.
As the fourth son received no part of the family wealth and had to earn his own, the martlet was also a symbol of hard work, perseverance, and a nomadic household.