My first question is about the galaxy map. When you click on a system, you receive information about the planets in system. Inhabited planets have up to four symbols: a small a picture of that planet, the symbol of the race controlling the planet, a smiley face indicating the planet's attitude towards ypu, and, sometimes, a mysterious fourth symbol not mentioned in the manual. In my current game, it's a yellow symbol that resembles a Gaalian hull. On page 29 of the manual, it resembles a hammer. What does it mean?

My second question is about equipment with special abilities like +2 to energy weapons or +3 fragmentation. These don't seem to create any noticeable effect. For example, I had a fuel tank that added +2 missile capacity, but having it installed didn't affect the capacity of my missile launchers. So, what, if anything, do special traits on equipment actually do?

If I'm not wrong that's a bonus to damage, not weapon capacity.

Been a while since I played but I'm thinking those 'extra' symbols denote the starbases in the system, such as military, pirate, science, etc.

The fourth symbol represents the planet's economy. Hammer is industrial, wheat is agricultural, etc. Economy type influences the prices planets will pay for different types of goods. If there's no symbol then the economy type is mixed.

You may be right if the translation is wrong (and it often is). But, IIRC, the bonus was called "+2 missile capacity".

That's what I meant to say. ; )

The bonus is indeed called Missile Capacity, but it affects missile damage. Mistranslation, clear and simple :)