This is a simple mod for Start10 that replaces the Start menu button with a Vault-Tec inspired one.  It is a Vault-Tec logo normally, then a Vault Boy when you hover over it, and a Vault Boy giving the thumbs up when you click on it.

Requirements:
Start10 (Start8 also has the ability to change your start menu icon, and there are other programs that do, too.  I've just only ever used Start10).
(Also, if you're wondering what Start10 is, it's a program that adds a Windows 7 style start menu into Windows 10, but with infinite customization options.  Only problem is is that it's $5).

Install:
Extract the .png image to your Start10 menu icon folder (default is C:\Program Files (x86)\Stardock\Start10\StartButtons).  Then, in Start10, go to this window and click Pick Image:



Choose the Vault Boy.png, and presto.  You now have a start button worthy of Vault-Tec!

(Note: This has only been tested on a 1440p monitor at 100% scaling resolution.  Higher scaling might make it look pixelated, depending on your resolution and screen size.)