Microsoft began displaying lock screen advertisements on Windows 8.1 PCs a few years ago, and the practice has continued with Windows 10.
These can be interesting at times, but they're usually a pain to deal with, especially if they replace a favorite wallpaper. Fortunately, they are simple to remove. Getting rid of these ads may also help with performance, as it is one less thing for your device to worry about (not that the difference will be much, but every little bit helps).
Select Settings > Personalization > Lock Screen after left-clicking on the Start menu. Select any option other than Windows Spotlight from the Background drop-down menu. Finally, scroll down and uncheck the box that displays "fun facts, tips, and more" on the lock screen. That'll be the end of any ads that irritate your eyes.