Z6 Prefix is Illegal

Within a recent ITU Operational Bulletin (#1149), it has been confirmed that the Z6 prefix is illegal.

Call sign series can be allocated only to the administrations of the ITU Member States by world radio communication conferences or, between radio communication conferences, by the ITU Secretary-General.

In this respect, the attention of the ITU administrations is drawn to the fact that ITU has not allocated call sign series Z6 to any of its Member States. Consequently, the utilization of call signs series Z6 by any entity without a formal allocation and consent of the ITU represents an unauthorized and illegal usage of this international numbering resource.
— ITU Operational Bulletin (#1149)