An iSCSI LU is a file within one of the server's file systems. Such a file must have an .iscsi extension to identify it as an iSCSI LU. However, apart from this extension there is no other way to determine that a file does indeed represent an LU.
Note: customer support recommends that all iSCSI LUs are placed within a well-known directory, for example /.iscsi/. This provides a single repository for the LUs in a known location.