Not only is it part of the name, it is a CRUCIAL part of the name. Otherwise, companies would not invest hundreds of thousands of dollars just to get each and every one, and that much again annually to protect them.
Any document signed without the 'LLC' is not binding to the company, and the individual signing is personally liable for its contents.
EDIT: In addition, when it comes to the legality/responsibility factor, the same would apply to the 'GS' - 'Goldman Sachs' issue. They would not be considered even related, inside any courtroom.