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: 
You can try something like [**UserInfoTip**](http://www.akslab.com):

> 
> * Select some files or folders, assign icons for them, and add a description to be displayed in Explorer's popup windows.
> * You can easily notice the marked files among other files and recognize their types by the icons.
> 
> 
> 

![1](https://i.stack.imgur.com/7MMul.jpg)  

![2](https://i.stack.imgur.com/o2q6s.jpg)  

![3](https://i.stack.imgur.com/WcouI.jpg)

---

Of course, nothing prevents you from [creating an Icon Overlay Handler](http://msdn.microsoft.com/en-us/library/cc144123%28VS.85%29.aspx) of your own. You can get started by using [TortoiseSVN](http://tortoisesvn.tigris.org/ExplorerIntegration.html)'s [code](https://stackoverflow.com/questions/843506/shell-icon-overlay-c), but remember that there's [a 15 overlay limit](https://stackoverflow.com/questions/4411336/shelliconoverlayidentifiers-why-so-few) (which will get exhausted in no time if multiple programs attempt to set overlays), and icon overlays are not even recommended by people such as Raymond Chen.
[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.