Two-letter signals for General Signal Code examples are listed below as they relate to casualties and damages. Single-letter signals should be allocated to significations which are very urgent, important, or of very common use. For web page layout purposes the signal flags are shown here horizontally. As a general rule only one hoist should be shown at a time. Each hoist or group of hoists should be kept flying until it has been answered by the receiving station. When more groups than one are shown on the same halyard they must be separated by a tackline. The transmitting station should always hoist the signal where it can be most easily seen by the receiving station, that is, in such a position that the flags will blow out clear and be free from smoke. A more complete list of two-letter codes is shown in Chapter 2, Section II of the International Code of Signals.
Two-letter signals for General Signal Code examples
Note: Two-letter codes use compliments. That's basically a number that provides a variation of meaning within a certain group.
Code
Meaning
HV
Have you been in a collision?
HW
I have (or vessel indicated has) collided with surface craft.
HW 1
I have (or vessel indicated has) collided with light vessel.
HX 1
I have received serious damage above the waterline.
HX 2
I have received serious damage below the waterline.