<p>I didn't get a photo of this band's main banner (if they had one) so can't remember where they're from, but "another visiting Washington-state band" is indeed a safe bet.
</p>
There were about a dozen flag-twirlers; as far as I can tell the graphic on the flag is of piano keys.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/8715708@N03">Brian Burger</a> from Victoria, Canada
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/wirelizard/5749357067/">Piano-key Flags</a>