Heraldic Beasts?

[Mike_Oettle]

Like Rathdown, I suspect that what Mark E is describing is a coat of arms, rather than a crest.
Although the word crest is commonly used to describe anything remotely heraldic, it is actually the topmost part of a heraldic achievement.
It sits on the helmet, which is why it has a crest-wreath (or torse) below it, or alternatively a crown or coronet of some sort.
This was because the crest was actually modelled and bolted to the helmet, and something was needed to conceal the bolts.
Crests are on occasion quite detailed (although that is usually the outcome of bad heraldic design), but generally they comprise a single charge, which can be animal, vegetable or mineral, and is quite often human (a head, a hand, sometimes a whole body, but more usually part of a body – the head and shoulders, or from the waist up).
The crest is commonly put on signets because it is a small emblem (by comparison with the shield and other elements in an achievement) and can more effectively be rendered at that size.
The more familiar use of the crest in Scottish dress is as a badge – when worn within a strap and buckle it is the sign of a clansman, and wearing it signifies submission to the authority of the chief whose crest it is.
Regards,
Mike