The following are important rules surrounding declarations. Breaching these declaration rules can make your declaration invalid, and hence be RDM.
You are not to declare on anyone inside a running vehicle or near a running vehicle over Direct Communication. An in-game message should be sent to declare.
Police that are speeding down a road with sirens on does not mean that there is an open declaration between you and him. In order for this to be a declaration on you, the cop must be sirening YOU / chasing YOU.
Bad declarations: Any declaration at a minimum must state an action for the other party to perform. Such as to leave an area immediately, or that if someone enters an area they will be shot. A bad declaration is something that might simply state: "All cops at Air HQ are dead." Declarations are situational, and should be clear and concise. The declaration should relate to the current situation, for example, if someone is in a vehicle, they should be told to stop/land and exit of such vehicle. Each declaration will be judged differently based on the circumstances in a game issues environment.
In the general scenario, a declaration only needs to state an ultimatum if it is not already implied. For example: telling an officer to leave an area you are in if you are wanted, or telling someone to land an aircraft when the obvious consequence is to be shot down. In the heat of the moment, it might not be possible to include the consequences for not complying and a roleplay reason. The obvious consequence for not complying with any declaration is death.
Hiding behind the declaration rules: If a police officer or security officer is clearly pursuing you, but they have not declared via sirens or other means, you are entitled to kill them, as they are a threat to you. You have to be 100% certain that they are indeed pursuing you by going out of your way to make sure the cop is pursuing you, such as driving through back alleys, avoiding main roads, etc. Killing a cop that you believe is a threat to you even if they are not actually pursuing you is punishable under the RDM rules. If you receive a declaration ingame that you believe to be invalid, you should not hide behind the declaration rules and not comply for this reason. Invalid declarations are to be dealt with in game issues, and if you are hiding behind the declaration rules in this way, compensation may not be provided when the issue is brought to game issues.
Hiding behind declaration rules also includes police responding to scripted or non-scripted events, such as checkpoint takeovers, banks, etc. If the police are clearly responding to the situation without declaring, you can kill them, as they are a threat to you. You can only engage on police in the immediate area of the event in this manner, not set up ambushes along the cops travel path and fire on them without another declaration. If you plan to ambush at their nearest HQ or along the road, a separate declaration must be sent following the above rules.
Terrorist missions: There is no declaration until the message containing the location of the mission has been sent to rebels pops up. If there should be any combat prior to the rebels being notified of the location, a separate declaration should be sent.
Faction Raids: A declaration on the police in/around a faction area is open from the moment the global message goes out stating that police are raiding your faction. This means that rebels can engage on police from outside of the faction area. Police can shoot out of the faction area at rebels if the rebels are doing any of the following actions:
Landing/stopping after you have fired warning shots near them.
Looking at you, armed or unarmed. (If they are unarmed, fire some warning shots before shooting them to give them time to leave).
Running towards the faction area while armed (such as they've landed on a hill and are running towards the area to attack/help their gang members)
These situations will be judged by admins on a case-by-case basis.