It was originally intended to be the graphic for anyone that earned the Childkiller reputation in Fallout 2, which is when one kills a young one. Some background info from the creator, artist Brian Menze, who not only worked on that game but is currently a part of the new Vegas expansion for part 3:
“This image was unused and the only Vault Boy image to ever be cut from Fallout 2. (I’m sure you can figure out why) I remember when I got the request to do a perk illustration for “child Killer” that there would be no way to keep in from being offensive. I mean really! How do you make an illustration of “child killer” and keep it from being offensive? Anyway for some reason, I thought this was the least offensive way to do it. I have no idea what i was thinking. Even the designer who requested it realized it was a bad idea, so we nixed it. Looking back on it now, I can’t believe I drew this.”
The image was recently posted on his DeviantArt, but quickly pulled, no doubt a request from his bosses, who clearly are still not comfortable with Vault Boy engaging in such a heinous act. But you know, post something on the internet for as little as 20 seconds, and it’s out of your hands forever. Via Hellforge.