I’ve noticed that chamberofcommerce.com uses OSM data on some pages (e.g.) with attribution message hidden behind a div. Who deals with these sorts of issues?
As a first cut, you do. Send them a polite message pointing out that the required attribution isn’t visible, include a link to Licence/Attribution Guidelines - OpenStreetMap Foundation If they don’t react within a reasonable time frame, ask again and then you can escalate to the LWG.
Here’s an example message text that you can use: Lacking proper attribution/Example email - OpenStreetMap Wiki. There are also translations into other languages.
But of course feel free to modify the text and make it personal. Just make sure it’s friendly. We want to encourage attribution, not scare them away from using OSM.