I'd suggest to include the trademarked logo/artwork only in the official images built by the VyOS(tm) project, and modify the build scripts to not include the official branding in self-built images - so it will be immediately obvious from the boot splash screen that the image is not official, and the user is alerted to use extra caution. It does not replace checking digital signatures, and a bad actor could theoretically make a broken unofficial image with official branding included, but that requires extra steps and could be considered intentional trademark infringement. The suggested change would help prevent accidental trademark infringement, and unnecessary confusion.

There is a precedent for something similar, see https://www.debian.org/logos/ - Debian has two logos, open-use one and restricted-use one. As I understand, unofficial modified Debian builds are not allowed to use the restricted-use logo.