Guys, it's as simple as this: if someone likes the looks of a military sporran but wants to be respectful enough to remove the military insignia, then they will probably replace it with some sort of civilian insignia in order to maintain the same overall look. For those of us here in the US, where civilians don't typically wear any sort of badges or pins on a regular basis, a clan badge is the easiest and most obvious substitution. They are sold everywhere that carries Scottish paraphernalia. And if a person has a clan affiliation, there's no question in their mind about whether it's appropriate to wear that badge. So that's typically what they will choose.

And yes, it is probably more common in the US to wear military surplus clothing and goods with civilian attire than it is in the UK. This is a cultural thing going back at least as far as the Vietnam War era, as I'm sure you know. It can take many forms, from a method of protesting to a simple statement of personal style. But it's not unusual at all. And for something as benign as a sporran - especially a simple brown leather sporran that isn't overtly militaristic - it's really quite understandable.