It's been talked about for years (advertising on stamps) but the USPS has generally abandoned the idea. Of course, as mentioned in the earlier post, some may consider some of the pop culture stamps to be commercial advertising in nature -- and let's not forget the Hershey's Kiss stamp, either.
Since this was posted in a non-country specific thread, the link below may be of interest as it relates to
Canada Post and McDonald's advertising both in their postmark and in the selvage of some of their stamps:
https://goscf.com/t/19975Other countries have done similar ads on stamps with varying degrees of success but not to the point that we can look forward to stamps bearing advertising logos anytime soon.