If you don't plan on installing macOS High Sierra for whatever reason, your Mac will still inform you of the software update every now and then via persisting system notifications.
How to stop “Upgrade to macOS High Sierra” notifications

If you don't plan on installing macOS High Sierra for whatever reason, your Mac will still inform you of the software update every now and then via persisting system notifications.
We reported yesterday that Apple is introducing a new privacy feature.
Aside from previewing the major new features and enhancements coming to your iPhone and iPad this spring via the forthcoming iOS 11.3 software, and releasing a barrage of new OS betas, Apple yesterday also dropped the Xcode 9.3 beta with some interesting new capabilities.
Enthusiasts have discovered that the macOS High Sierra 10.13.4 developer beta code comes with subtle hints at a desktop Podcasts app, possibly indicating that podcasts might be unbundled from iTunes in favor of a standalone app.
Apple on Tuesday seeded the fifth beta of macOS High Sierra 10.13.3 to developers. The update can be installed by registered developers using the Mac App Store's update mechanism.
Anyone with physical access to your Mac with macOS High Sierra 10.13.2 is able to access and change your App Store settings in System Preferences without entering a legitimate password.
Apple on Monday launched the second beta of macOS High Sierra 10.13.3 to developers. The build number is 17D25b, and the update can be installed by registered developers using the Mac App Store's update mechanism.
If your iMac Pro is refusing to boot following a power failure during a macOS software update or has stopped functioning properly, which may happen in certain circumstances, you might need to perform a DFU-like restore process using a secondary Mac and Apple Configurator.
Apple on Monday launched the first beta of macOS High Sierra 10.13.3 to developers. The build number is 17D20a, and the update can be installed by registered developers using the Mac App Store's update mechanism.
On December 6, 2017, Apple released macOS High Sierra 10.13.2 to the public following a month of testing. The free software update brought under-the-hood enhancements, but no new user features or other outward-facing changes were added in the release.
Apple on Wednesday released macOS High Sierra 10.13.2 to the public, after a month of testing. This marks the second update for macOS High Sierra, and it can be installed via the Updates tab in the Mac App Store.