In Lightroom, simply moving files to another folder does not add a logo or watermark. Watermarks are normally applied during Export, Print, Web, or Slideshow output. So the most likely cause is that the photos were exported with a watermark and then possibly re-imported.

If that’s what happened, Lightroom usually can’t remove the watermark from those exported image files because it has been baked into the exported copy. You would need to go back to the original, unwatermarked files in your catalog and export them again without the watermark option enabled.

If the logo somehow appears as an edit on the image you’re viewing, select a photo in the Develop module and check the History panel on the left. If there is an earlier state before the change, you may be able to revert to it. But Lightroom does not normally add logos as a Develop adjustment.