Question: Is there a way or a program that marks the icon of a file with a badge, similar to how Dropbox marks synced files with a green checkmark, and files that are currently syncing blue?

I'd use that to mark videos I've watched in a series.

Answer: 
I couldn't find a better solution, so I've created an open-source project for that. Available at <https://github.com/csomakk/IWatchSeriez>
Its nothing special yet, but it does the trick, and I'll try to work more on it. I Watch Seriez, IWatchSeriez :)

![enter image description here](https://i.stack.imgur.com/CmmqI.png)
[See this image](https://i.stack.imgur.com/u7AqA.png)

Click, show the hidden files from the folder options and hide the file you already viewed. Since you enabled to show the hidden files from the folder options windows will show the hidden files by blurring it. This way you can mark the viewed files See the photo attached that the DNA and RNA file is blurred.