Alfa Romeo Neon-like LED Sign

It’s a very nice sign. The blue color I chose has a nice glow, but I’m confused because there was a black plastic I assume it’s a backing plate, but there were no instructions whatsoever so I managed to get it against the back of the thing and then use pushpins to put its bottom part into the wall, but you folks really need some instructions because that thing wouldn’t just adhere to the back of the sign .