I always wear a kilt pin myself. An interesting question is what makes the difference between a pin and a brooch? I have a feeling that it's partly shape, and partly size. Most brooches I've seen are larger than kilt pins and rounder in shape, though I've seen paintings dating back a century and a half or so where very brooch-like kilt pins are worn.

Another thing I've noticed in these paintings is that the kilt pin is normally worn much higher on the apron, about halfway up. Does anyone know the reason for this? It's not only in those old paintings either by the way, I've seen a picture from Prince Charles' and Diana's honeymoon in '81 where he wears a safety-pin type kilt pin in the same place.