According to the regulations of the ITU, in particular of article 19 of the Radio Regulations, “Identification of Stations“, all stations whose ranges exceed national frontiers must be identified by a call sign in accordance with the series of call signs assigned to each country and be registered in the International Frequency List. The series of call signs assigned to the Federal Republic of Germany begins with DAA and ends with DRZ. For the DCF77 transmitter, the call sign has been determined as follows: In accordance with the series of call signs assigned, D stands for Germany. The letter C was selected to identify long-wave transmitters. As a third letter, the letter F was determined for the long-wave transmitters on the premises of the transmitting radio station Mainflingen (due to the vicinity to Frankfurt). As the transmitting radio station Mainflingen uses several frequencies in the long-wave region, the numbers 77 corresponding to the carrier frequency 77.5 kHz were added to the three letters DCF to distinguish between the different transmitters of that station.
As a clear assignment of signals to the DCF77 transmitter is always possible due to the characteristics of the DCF77 signals, emission of this call sign has been given up since 2007 in agreement with the Radio Regulations.