I've seen sometimes when people working under temporary contract open pull requests declaring the sponsorship in the PR description. IMO it's fine, and actually nice and modest way to show the opensource contribution of private business entities.
What about posts on *ros.org, e.g. here discourse and answers?
I've seen a few times that someone put links to the products of (supposedly) her/his own on their answers posts, then got removed by moderators. I agree that obvious sales ad like that are not suitable on opensource forums. But what about sponsorship that enable the content of the posts?
My temporary part-time employer requests me to add the sponsorship on my posts that are related to their service but I'm just unsure, and afraid that micro-level notation like that could rather give more negative impressions.