You are correct you can hit ignore, and then the more you hit ignore the faster they come up and prompt. I have 5 on my desk right now that after you hit cancel to the sign in page it pops back up in 1 minute putting itself in the foreground so you have to deal with it. Try getting anything productive done if every 1 minute you have to stop doing what you are trying to do and click the No button. It is very annoying and they have just pulled them out of their room. The only good news to come from this issue is they are going to actually spend the money to extend my Jamf licenses from just the iOS and tvOS devices to also include the OSX devices as well so they can actually start using the Mac's again.You can easily run an iPhone or macOS without iCloud. Apple of course suggests you login but can easily be skipped on install or first boot without any nags. iCloud gives a tremendous amount of user benefits but Apple doesn't force anyone to use them.
A lot of anti-Apple bias.