Every Jet Fighter these days seems to have a Head Up Display. What do all of these indicators mean?
Some things are fairly obvious:
there is a compass
there is an artificial horizon
Other things are less obvious, i.e. what is this _ / \ / \ _ ?
HUD symbology varies depending on flight mode and aircraft configuration so you will find a wide variety of symbols capable of being displayed. Some basic ones from the F/A-18 E/F aircraft are.
To your original question the ‘W’ symbol is called the Waterline symbol and represents the point at infinity where the longitudinal axis of the aircraft points toward. It is analogous to the miniature airplane symbol on an attitude indicator. A similar symbol called the Gun Cross is used on the F-16 HUD.
On high performance aircraft capable of high AoA operations, the waterline symbol is not as useful as the Flight Path Marker or Velocity Vector symbol which indicates the point at infinity the aircraft is currently trending towards.
Can’t answer your specific question but I can tell you HUD symbology is often unique to each Service, type aircraft, and manufacturer, so it is possible the specific symbols you are asking about are known only to the pilots, avionics technicians, aircraft software developer, and the small team of military and contractors that acquired and tested the symbology for that aircraft type and model.
Some symbols have evolved to be common across manufacturers but much is unique to fulfill the military customer’s requirement.
So the symbols you ask about could represent vertical or lateral guidance cues, etc. Typical military HUD symbology includes flight parameters such as airspeed, altitude, vertical speed, heading, etc.
Usually critical aircraft system parameters such as engine temperatures, power, etc. are also normally displayed, or at least there are warnings that pop up when display space is limited. Weapons info is also displayed if applicable.
The trade off between space available on the display and what’s deemed required to be in view, without too much clutter, is always in play. This is especially tough when the HUD is helmet mounted as is often the case with military helicopters. That’s a small piece of glass.
Hopefully someone that developed or flew that particular HUD will respond.