My guess is that it was the front side of a lit sign. Probably had some opaque material behind the letters to diffuse the light source.That being said, it may be too small for that.
I agree that it was cut using a CNC plasma cutter, you can see where the metal is discolored from the heat of the plasma cutter, so it's not old and was done by someone with access to the plasma cutter where he/she worked, my guess is that they like beer, especially Miller beer!!
Yup! Definitely a plasma cut. It's too rough/dirty to be laser or water jet cut. I have 2 plasma tables less than 50 feet away from me. I'm pretty familiar with the process.
My best guess on the material would be 1/4" thick stainless steel. Probably 304, maybe 316 or 303.