damage (position player nearestObject 274849) >= 1
Where the number sequence is the id number of the object in the editor. Just replace my "274849" sequence with your wanted id number and it should work. The nearestObject thing is a needed workaround in Armed Assault, not sure if they fixed this in ArmAII or not. In that case the old OFP solution should work as well, but I doubt it.
damage (Object 274849) >= 1