I use the awesome Bigbox function to display marquees on a secondary monitor. For years I've been collecting high res Mame arcade marquees from all over the internet. Not all marquees are in 4K but many are, I've down scaled the resolution to max 3840 pixels wide and saved all in .jpg format for a good size and quality balance. This could be the largest high res marquee collection out there, not sure. Some game marquees could be missing. 1398 marquees total.
I have forgotten where I got all marquees through the years but I know many came from the legendary @Mr. Do collection see: https://mrdo.mameworld.info/index.php
@ArsInvictus is certainly one of the providers as well.
If you see anything you've worked on please let me know so I can tag you here for credits.
Hope you enjoy this collection.