Yes, I would have thought that such logos would be trademarked. Wikipedia pages like this, though assert the following:
This image consists only of simple geometric shapes or text. It does not meet the threshold of originality needed for copyright protection, and is therefore in the public domain.
Given the complications, your respond when necessary approach sounds very reasonable. Also given that I’m not making any money, it seems unlikely that a complaint would arise.
Also, I did not consider the possibility of URL structure changing.