: It was made soon after Glaurung first emerged from Angband (First Age 260). The helm itself was not actually shaped like Glaurung -- it merely had a crest shaped in the form of Glaurung's head, which was gilded.

Fair enough!

: : Another possible reason which has occurred to me is was it an
: : apotropaic symbol. This is the use of a frightening image to
: : avert evil. Mediaeval churches had gargoyles and monstrous
: : images on the outside to frighten away evil spirits. Could the
: : dragon on the helm have had a similar use?

: I can accept without argument the notion that Tolkien might indeed have been drawing on Anglo-Saxon influences in letting the Dwarf-smith Telchar put a dragoncrest on the helm (it would be absurd to discount A-S influence in all areas of Middle-earth), but I draw the line at Medieval mysticism and superstition unless there is some textual support for the notion.

Draw no lines on the grounds of Mediaevalism! Apotropaic symbolism is essentially a universal human trait. The classical cultures were much addicted to it - the Medusa-head being one of the most often used. Charms in the shape of a hand making the "Horns" (a closed fist with the index and smallest fingers protruding) were commonly worn to ward off the "Evil eye." Amulets in the form of a phallus were also used to the same ends. A modern charm, in the form of a tapering sinuous cone, is usually called a "Horn of plenty" but can be traced back to Roman originals which are representations of a goat's phallus.
Indeed Sauron could be seen as a manifestation of the "Evil eye" writ large :o)

: Tolkien seemed to delight in reworking the old folklore traditions, but there is nothing like a gargoylic architecture or artistry in Middle-earth of which I'm aware (and I base that statement on what I've seen of Tolkien's own artwork).

: "Narn i Hin Hurin" says Telchar put the crest on the helm in defiance of Glaurung. I would say that, since he made it for Azaghal of Belegost, it was a sort of mark of prey -- Azaghal in donning the helm would be saying, "I hunt this beast". And as it turned out, Turin, the last owner of the helm, did hunt and slay Glaurung.

: I'm sure I've seen a word to describe that sort of hunting tradition, but dang me if I can think of it.

: Anyway, it may not have been intended so much to safeguard against evil as to mark it for the hunt. This vaguely reminds me of a shamanistic perspective, but I'm not sure I'm remembering that correctly. It's possibly a clue to Dwarven mysticism, when considered in this light.

There is a very famous Old Stone Age painting of a man dancing wearing the mask and antlers of a stag. Other images show various animals wounded by spears and arrows - I think this type of thing is described as "Sympathetic magic." It does seem a reasonable explanation for the existence of the Dragon Helm.