Which of the following is NOT a name of a "signpost" in a MARC 21 record?

In the context of a MARC 21 (Machine-Readable Cataloging) record, "signposts" refer to elements that help organize and identify data within the record. The terms commonly used include fields, tags, and indicators. A field is the primary data unit in a MARC record, while a tag is a numeric code that uniquely identifies the type of information contained within that field. Indicators are specific characters or codes within certain fields that provide additional information about the data.

The term "call number," however, does not represent a structural component within a MARC 21 record. Instead, a call number is an identifier assigned to a book or resource that helps to physically locate it on the library shelves. It plays a vital role in the organization and retrieval of physical materials but does not function as a signpost in the technical structure of the MARC record. Therefore, it is not classified as a field, tag, or indicator within the MARC 21 system.