ISO/IEC 15424:2008

The need exists to identify the data carrier a reader detects in autodiscrimination environments. The Symbology Identifier concept provides a standardized way for a device receiving data from a reader to differentiate between the data carriers. ISO/IEC 15424:2008 deals mostly with bar code symbologies; the terms Symbology Identifier, symbology, and bar code are therefore used throughout ISO/IEC 15424:2008 although they are intended to apply to other data carriers as well.
This identification is achieved by the addition of an optional feature to readers enabling the reader to prefix a standard string of characters to data messages. This preamble contains information about the decoded symbol (or other data carrier) and any processing the reader has done. The information is not encoded or otherwise explicitly or implicitly represented in the symbol, except that the presence of some optional features may be detected by the reading equipment, whereas others require the reader to be expressly configured to implement them.
ISO/IEC 15424:2008 should be read in conjunction with the relevant symbology specifications.
ISO/IEC 15424:2008 applies to automatic identification device communication conventions and standardizes the reporting of data carriers from bar code readers and other automatic identification equipment. It specifies a preamble message generated by the reader and interpretable by the receiving system, which indicates the bar code symbology or other origin of transmitted data, together with details of certain specified optional processing features associated with the data message.