On the pic of John Brown and the piper the "brooch" doesn't seem to be on the apron but to the side, could it even be a buckle placed part way down to preserve modesty, it would make sense either way but the placement is what pushes me towards the buckle route.

Personally though, the term "Prince Charlie" always brings views of a small syphilitic italian wearing a womans dress and making a big deal about travelling across a short stretch of water to Skye. As my Fiancee said when she first saw the "sea to Skye".
"Why did she use a boat, she could have thrown him across."