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)

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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.
I was searching for a similar solution when I found this thread. I figured out a fairly simple way to achieve what you're looking to do (at least in this particular case.) Maybe it will help others that happen upon this.

If you have the appropriate permissions, you can view "Hidden" files in Windows. They show up as grayed/semi-transparent icons/thumbnails of the original. 

First, be sure that you're able to see Hidden Files. 

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1. Open Folder Options by clicking the Start button , clicking Control Panel, clicking Appearance and Personalization, and then clicking Folder Options.
2. Click the View tab.
3. Under Advanced settings, click Show hidden files and folders, and then click OK.

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Now all you need to do is right click each episode after viewing it, go to Properties, and check the "Hidden" box. It will remain there but grayed out, allowing you to keep your place! 

Cheers!