Well, technically, in the UK, it is illegal to wear the Balmoral tartan, let alone sell it, since it is a restricted tartan. Wearing the Balmoral tartan is kind of like the kids you see wearing military insignia that they are not entitled to: in the US, it is technically against the law because you impersonating a soldier of the US military, but whose going to enforce it? Nevertheless, I have mentioned to kids that I see wearing medals and combat infantryman badges (CIBs) that a veteran who earned that insignia might not be as generous with their response to them.

The bottom line is respect for tradition and custom. Wear what you want to, but as Jimmy says, be aware of what you're wearing and be able to defend why you're wearing it.

Cheers,

T.