Any offensive weapon can be used in the killing blow; Drone, bomb, missile or a turret of any kind.
Furthermore the following restrictions apply:
- Killmarks are not awarded for destroying capsules, Shuttles, Rookie Ships, unmanned vessels, structures, cans(containers), wrecks, drones or NPCs.
- Kills against corp mates will not produce a mark.
The style of the marks themselves is determined by the manufacturer of the ship; Gallente ships display Gallente-themed kill marks and so on.
If a player repackages their ship then the killmarks will be removed. Should such an event occur then players can contact Customer Support and request that their kill marks be restored. They are advised to contact support as soon as possible after the repackage takes place and to retain possession of the ship.
Some players may opt to sell their killmarked ships via contract (reselling via market will require a repackaging and thus the erasing of any killmarks on the ship).
Any ships accepted through contracts would be done so at the discretion of the buyer. Any information supplied by the seller concerning kill marks may not be entirely accurate.
More information is available in the Dirt & Killmarks - Dirt and Destruction in New Eden dev blog.