Jon Chase, in his review of the new HomePod for Wirecutter:
An unhappy discovery after we placed a HomePod on an oiled butcher-block countertop and later on a wooden side table was that it left a defined white ring in the surface. Other reviewers and owners (such as Pocket-lint, and folks on Twitter) have reported the same issue, which an Apple representative has confirmed. Apple says “the marks can improve over several days after the speaker is removed from the wood surface,” and if they don’t fade on their own, you can basically just go refinish the furniture—the exact advice Apple gave in an email to Wirecutter was to “try cleaning the surface with the manufacturer’s suggested oiling method.” This really undermines the design aspect of the HomePod—especially if you were thinking of displaying it on some prized piece of furniture—and it will surely be a sore point for many potential buyers. In other testing, we have seen no visible damage when using it on glass, granite countertop, nice MDF, polyurethane-sealed wood, and cheap IKEA bookcases. We also tested the HomePod in the same place a Sonos One regularly lives—and the Sonos hasn’t caused damage in months of use.
It’s amazing this wasn’t caught during Apple’s testing of this device in employee’s homes and the company’s labs. Not great, Jony. Not great.
Update: Apple has updated its “Cleaning and Taking Care of HomePod” kbase article:
It is not unusual for any speaker with a vibration-dampening silicone base to leave mild marks when placed on some wooden surfaces. The marks can be caused by oils diffusing between the silicone base and the table surface, and will often go away after several days when the speaker is removed from the wooden surface. If not, wiping the surface gently with a soft damp or dry cloth may remove the marks. If marks persist, clean the surface with the furniture manufacturer’s recommended cleaning process. If you’re concerned about this, we recommend placing your HomePod on a different surface.