When I was a kid I once found a cassette tape on the street when I was mowing the lawn. I took the cassette inside, hoping it would have some juicy stuff on it such as someone’s “audio diary” or something of the sort. Turned out to be some recording from a meeting- BOOORING!
If I found an unlabeled or mysterious-looking CD and it didn’t have any big physical defects I’d stick it in an audio player. If it had computer data on it I’d only stick it into the drive on my old system, which doesn’t contain any vital information. If the disk contained viruses or other bad data I could simply reformat the hard drive and re-install the OS.