I think this picture has been posted here before, but I know that guy. He was in the gun club I was in when I lived in northern Va. He usually had that on a tripod aimed at his front door. He was one of the folks I knew who worked for the company that put the back door in openssl, and being hired to do that by the FBI turned everyone I knew there kinda paranoid.
Apparently the armorer's manual for that has a comment that says while it's not particularly effective against tanks, it's great for morale.