Clan Badges as Kilt Pins?

[Wompet]

I've been rooting around EBay a bit this last week for kilt pins, and there's something I keep seeing. In among what I've always thought were kilt pins (elongate form, normally sword- or cross-shaped, with a long pin on the back) are circular clan badges (the "belted" clan crest).

Are these mistakes (intentional or accidental) or the part of the sellers, or is it appropriate to wear a clan badge as a kilt pin?

And if it is appropriate, are there other acceptable alternatives to "traditional" kilt pins? I remember seeing a stuffed gecko in Daneel's gallery, for instance. And of course there's the "XMarks" kilt pin, too ... ??: ... Let me rephrase the question - what have the folks here used as acceptable alternatives?