A signaling strategy is, in game theory and in particular grand strategic interaction, a set of measures that do not directly compel or deter an opponent, but attempt to demonstrate that the opponent's continued action will lead to consequences that the opponent does not want. It was a major part of the model of communication between the United States and North Vietnam during the Vietnam War, especially espoused by Secretary of Defense Robert McNamara.
For example, the initial bombing campaign against the North, Operation ROLLING THUNDER, deliberately began with inconsequential targets and gradually went to more important ones, to signal the inexorable determination that the United States would continue to increase pressure until it compelled the North Vietnamese to stop infiltrating the South. There was an implicit assumption that the North Vietnamese Politburo would hear and respond appropriately to the signals, yet postwar analysis suggests they were not even aware of them.
This assumption drew from the compellence theory of Thomas Schelling. Lyndon B. Johnson refused to allow the most valuable installations, those around Hanoi and Haiphong, to be attacked. The idea was that damage future was more harrowing than damage present. In practice, the slow escalation gave Hanoi time to camouflage and decentralize its installations, and thus minimize the damage.The raids were closely controlled by the White House, which saw them as "signals" in a negotiating process with Hanoi. There is no indication, however, that Hanoi even perceived that signals were sent.
Raids were calibrated so that each month they became more punitive, at least in the American value system. This theory, centered in the Office of the Secretary of Defense, was that sooner or later Hanoi's pain threshold would be crossed and they would agree to negotiate a plan that would allow South Vietnam to survive.
A classic error, which generations of professional intelligence analysts have been taught to avoid, is mirror-imaging. The Johnson Administration treated the North Vietnamese as mirror images of themselves, rather than people with a radically different mindset.
At the time, the Joint Chiefs of Staff had recommended a quick campaign of much more intensive bombing, which would send a much less ambiguous message and also directly interfere with the warmaking ability of the North. 
In retrospect, one of the stranger signals was sent when the U.S. detected surface-to-air missiles (SAM) in the North, but deliberately did not attack them while they were vulnerable in transit or assembly. The signal being sent was that the U.S. showing restraint should be countered by the missiles not being used. The first SAMs were detected in early April 1965. Civilian staff in the Department of Defense refused permission to attack them. John T. McNaughton, assistant secretary of defense for international security affairs, said, “We won’t bomb the sites, and that will be a signal to North Vietnam not to use them.” On a visit to Vietnam, McNaughton told Moore at 2nd Air Division, “You don’t think the North Vietnamese are going to use them! Putting them in is just a political ploy by the Russians to appease Hanoi.” A political ploy, presumably, shot down a F-4C fighter-bomber flown by the United States Air Force. 
- Schelling, Thomas (1963), The Strategy of Conflict, Harvard University Press, p. 195
- The document listing these targets, 7 Sep 1964 JCS Talking Paper for CJCS, "Next Courses of Action for RVN" indeed starts with 1 and ends with 94, but it only contains 93 distinct targets
- , Cable from CINCPAC to the Joint Chiefs of Staff on Proposal for "Next Courses of Action in Southeast Asia", The Pentagon Papers, Gravel Edition, Volume 1, Volume 3, pp. 542-545, Volume 1, Chapter 4, "U.S. and France in Indochina, 1950-56", Section 3, pp. 314-346
- Correll, John T. (March 2005), "Rolling Thunder", Air Force Magazine