Re: "What does digital signage show when humans aren't around?"
...my registry is probably the thing of nightmares!
Ccleaner. It's been keeping my current once-was-XP-now-10-on-entirely-different-hardware-but-for-the-case setup tidy for years.
My favourite giggle is to take a brand new, freshly "gold imaged" corp machine and run Ccleaner over its registry to see how much cruft there is. I always get a potted history of the image's gestation with remnants of each and every piece of software ever installed for test or pilot, along with a good feel for how repellently shite their uninstall processes were. Always horrific to see what the "professionals" think is perfectly OK.