In fact, except in the case where the VIP and Decoy are of different genders, both the VIP and Decoy will be completely undistinguishable from one another. This is obviously the intention, if the enemy does not know which players is the VIP and which is the Decoy, they must expend effort trying to kill them both. A good Decoy will try to catch the enemy's attention to get them to try to attack his location. But keep in mind when you are playing the Decoy, that you should try to make your discovery seem 'accidental'. In general it is probably best to rely on your Decoy to claim most of the bases so that your VIP is not placed in jeopardy.
Decoys are worth one point when they are killed.
As mentioned before, there are no static 'team' bases in VIP Assassination. Instead your team spawns out in the open with no base and must claim one or more bases from those available on the map. Either your Decoy or VIP may claim bases, standard players will be unable to do so and will only receive a warning if they try. There is a limit, specified in the mission file, to how many bases you may control at once. Once you have reached that limit you will be unable to claim any more bases.