Since this discussion arose with a question regarding crest beasts, let me revisit that particular aspect.
It was asked how one could distinguish between heraldic beasts and others.
Since we are talking here about animals forming part of a crest, let me point out that while heraldry has any number of extraordirary beasts not (much)encountered elsewhere, almost any animal can be pressed into armorial service.
Leaving aside the question of whether a particular crest is legallyyours (which has been covered in depth), bear in mind that a crest on a signet ring will invariably be shown emerging from a crest-wreath or torse, or alternatively a coronet of some kind (usually a crest-coronet, also known as a ducal coronet),
If such a wreath or coronet not only appears beneath the animal, vegetable or mineral devic, iti dentifies it as being part of a crest.
On a signet ring such adevice would appear without colour (although it could have Petra Sancta markings on it inidicating the colours).
So while it might have been carved to represent an entirely different family, if it shows your family's crest it can be regarded as belonging to your amily.
In some instances Lyon Court or the College of Arms has granted distinct crests to members of the same family, In other cases the same crest serves for several armigers of the same family.
If I find a crest-badge in plain metal which shows a demi-kudu issuant, I could make use of it as a representation of my own crest. and wear it on my bonnet.
Regards,