A number of HomePod owners have started noticing rings left on wooden surfaces, particularly those with oil-based finishes. The silicone in the base of the HomePod can react to oil on a molecular level, causing these marks or rings.
This type of problem is not specific to the HomePod, in fact, all kinds of speakers (or anything with a silicone base like an Amazon Echo Dot) can cause these kinds of marks on wood. Because of this, Apple has updated its HomePod support page with the following information regarding the HomePod and wooden surfaces.
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.
Apple offers the following advice if you had your heart set on putting your HomePod on a 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 manufacturers recommended cleaning process. If youre concerned about this, we recommend placing your HomePod on a different surface.
Ironically, When Apple announced the HomePod, it showed it off on a wooden table. It is likely that Apple didn’t anticipate its new speaker wouldn’t play nice with wooden finishes.
Source: Apple WWDC 2017
If you still insist that the perfect place for your HomePod is on a wooden surface, you might consider some kind of barrier between the base of the HomePod and the wooden surface. Perhaps lining the bottom with felt material or even a cork material could protect your furniture.