It is interesting to note that indicators of behavior are very common, and that with a little imagination – or, even better, a great deal of imagination – we can learn a lot about the activities that the indicators point to from these seemingly non-related events.
A classic example of this in the private sector is the success of the televised appearances of political candidates. While the networks can give estimates of the number of people watching a given show, it would be nice to know if people were actually watching your candidate, or paying no attention at all.
There are a many ways one might approach this. For example, one might, during or after the event, call and ask people whom they watched. In certain circumstances one might be able to actually observe subjects in situ and note what they are doing.
Thinking more creatively, however, one might look at indicators rather than at direct actions. In the political candidate example one might get measurements of fluctuations in water pressure in an area’s water mains.
Why would this be an indicator? Well, in a campaign of significance, a significant number of people are watching the candidates on television. When the viewers are actually interested and watching, they are, well, watching, and are less likely to do other things. When they are less interested in the candidate they are likely to get up and go to the bathroom. The flushing of a lot of toilets causes a measurable fluctuation in the water pressure, which is something that the water department tracks. This can tell you which candidate is getting the greater (or lesser) amount of attention.
While this is interesting, from an OPSEC point of view its importance lies not in knowing about water pressure drops, but in understanding that there are many secondary indicators that give your adversary essentially the same knowledge as does direct information, and that you need to think about these carefully. In looking at the public sector, for example, it doesn’t take a mind reader to know that some important event is taking place if the Pentagon parking lot is full at midnight, and pizza trucks are going in and out.
The same is true of the activities surrounding what you do, which is why an OPSEC audit can be so fruitful.