That's pretty cool--I've got the same Penzoil "Sound Your Z" sign as HIRISC (it came off my uncle's barn) and the same Champion Spark Plugs box that Duece has. The box was never hung up before I got it a few years ago, but it didn't come with a key either. I should have one made.
I've also got a pair of Gulf gas station price signs: metal, with "Gulf NoNox and Good Gulf" on them, and a spot to hang the price next to the gas letters... 2-digit numbers, from 19-cents to 40-some centers. They're all metal, with enamel paint. Got them when I moved here to Georgia 5 years ago--my first week in town, was driving around and saw them outside an old gas station, laying against a seat. Asked the guy about them and he sold the whole set to me for $35--they'd never been hung up, and still had the paper between the number panels.
A few years ago I went home for Thanksgiving, and when we rolled into town on Tuesday evening, the Sunoco station I always filled up at was empty, but people were working inside. The next day I came back with $35, my dad's 12-foot ladder and his cordless drill to take the 24-inch tall SUNOCO letters off the wall. The hornets that were living behind the letters were not happy. I got stung about two dozen times, got some wasp killer and went back up and got my letters! They're spaced in my shop about a foot apart, and command a pretty big space on my wall. What's really funny is it turns out I ended up working with a guy who also grew up in that town (we're NE of Atlanta, the town was outside Toledo, Ohio), and he used to fill up at that station too.
-Brad