For publications, I think you'd be safe in using their logo as long as you were legitimately in the publication. Some sort of editorial content, not advertising

For publications, I think you'd be safe in using their logo as long as you were legitimately in the publication. Some sort of editorial content, not advertising. For users, I'm in the "it's better to beg for forgiveness than to ask for permission" camp. I've only had one company ask that their logo be taken down, mostly because they didn't want their competitors to know they were using us. You might even want to A/B test to see if having that on the page helps. If it doesn't improve conversions then it's probably not worth the risk of an angry customer. That being said, you might get more value out of asking for a testimonial than just putting a logo up. I recently did that and ended up having a few fall off the wagon due to needing higher-up permission. But the one's I got made it worthwhile.