What would the number 1090 indicate?

The number 1090 is an example of a coast station SITOR (Simplex Telex Over Radio) SELCAL (Selective Calling) number. SELCAL is a system used to alert an aircraft or ship of an incoming message on a particular frequency, allowing the operator to avoid constant monitoring of radios. This number indicates a specific coast station's unique identifier within the SELCAL system, enabling communication protocols that are essential for maritime safety and operations.

In this context, understanding that SELCAL numbers are formatted typically in a specific way helps clarify why 1090 would represent a coast station designated for such communication. The other options involve different identifying numbers for ship stations’ DSC MMSI or NBDP SELCAL numbers, which are distinct from coast station identifiers like 1090.