Note that it's not actually a letter 'M', but a backwards 'N'. I actually think it's the same thing with the letter 'S', rather than a 'Z', although it could well be illiteracy and confusion with that final 'S' sounding like 'Z'. I kind of think the 'G' is actually just a sloppy 'C', too. Note the sloppy brushwork on the serifs of 'E', 'B' and 'L'.
As Probus mentioned, the person who wrote the sign has some literacy issues, or sloppy writing at best. I'm sure it was done intentionally as a movie prop though, so it's hard to say for sure what they were trying to depict.