Here in the northeast USA most clans carry a tartan banner during parades unless the clan has a specific flag. For example the Clan Buchanan have a black rampant lion flag, the Sinclair have a black and white cross etc. But for the most part they are simply tartan fabric on a pole.

Here most clan put a vinyl name banner on the tent. Some have the clan badge or crest on it as well. We carried this horizontally tied to a pole in the NYC parade to identify the Clan but we also carried our banners on poles as well.

In other parts - esp. down south, you see a shield shaped banner with the clan name, crest and tartan hanging from a pole. But not so much up here.

There are no laws governing coat of arms in the USA. But tradition and respect would say that you shouldn't display the registered COA of a Chief or other person. Safer to stick with a crest or badge I would think.

Aye