What is it?

[MacKenzie]

The RedHead showed me this on reddit. Poster was asking what it is. Beats me.

[EagleJCS]

A tartan nappy/diaper cover?

A search for the Clan Mar brand didn't return anything, just the Scottish Clan Mar/Marr.

Modern nappy/diaper covers don't have the buckles.

[Darrin1200]

Maybe a kilt for a puppy.

[bdkilted]

Yes, it looks like a dog coat to me.

[Tony]

I'm thinking it could be one part of a two piece - the buckles don't appear to have a matching strap.
If it were for a dog, this would have to be on top or that big semi circle would just flap down.

[Ayzala]

Could it be a bonnet of some kind. The long piece at the top and the sides fold down. The two tabs at the top fasten into the buckles on the sides?

[Ninehostages]

That's the famous Stewart loin cloth.

Everybody needs one of those.

[Tobus]

I'm thinking it could be one part of a two piece - the buckles don't appear to have a matching strap.

It kind of looks like the two tabs on the short piece (extending outward from the tag) are crinkled like they fit into the buckles. Maybe just a friction fit into the buckles, since I don't see a prong on the buckles.

Is this some sort of device for a belted plaid?

[jhockin]

It might be helpful to retake your photos, with yardsticks alongside, to show length and width.

[MacKenzie]

Not my photos.