The main device (symbol) in the Durburgh blazon is the dolphin. The main tincture (color) is sable.
Sable, the deep black so often found in Heraldry is believed to named from an animal of the marten family know in the middle ages as a Sabellinœ and noted for its very black fur 1. In engravings, when colors cannot be shown it is represented as closely spaced horizontal and vertical lines, and appropriately is thus the darkest form of hatching, as this method is known 2. Although it may seem a sombre tone, and does indeed sometimes denote grief, it is more commonly said to represent Constancy 3.
In the days before television and the internet it was a rare heraldic artist that had ever seen a dolphin for real, so we should not be surprised that the heraldic representation is not instantly recognisable. Despite this, we should not forget that these artists considered the dolphin to be the king of fish, playing the same role as the lion in the animal kingdom. 4 For reasons not immediately clear, Wade suggests that the dolphin was regarded as an “affectionate fish, fond of music”. 5