Documents are divided by organ. It is important to understand the functions of the main organs, because many research sources are divided by organ, and are not cross-searchable. Document symbols are as follows:
A/- for General Assembly;
S/- for the Security Council;
E/- for the Economic and Social Council; and
ST/- for the Secretariat.
(More symbols can be found here).
Certain subsidiary organizations have their own document symbols. For example CRC/C stands for the Committee on the Rights of the Child. Only some of the documents with such symbols are official UN Documents. Some subsidiary organizations' documents may be internal documents only. Although the subsidiary organizations can still assign document numbers to these documents, they are not considered UN Documents and are not part of the depository system. These documents may be available through the subsidiary organizations, but are sometimes not available at all.