Indexicality

Indexicality is the way we can communicate things indirectly to your players, albeit this relies a lot more on intuition rather than conditioning. What this means is that players won't have a "cause-and-effect" learning experience to advice what could happen.

Resorting to this will rely heavily on the players' previous baggage and outside experiences, let alone the experiences they've had previously with the game, while not being entirely contained within your mission.

To put this simply, smoke cannot exist without fire, but it is not fire. The presence of smoke lets us know, indirectly, that there is a fire nearby.

Following this same logic, if we have some knowledge of previous missions, real life events, in-game universe lore, and even our users' backgrounds, it would be possible to try and put together things we know they might expect.

If players are sent out on a mission to rescue a crashed down helicopter, smoke is a good indicator of where there is fire, indicating where there is likely a crash. If players are trying to find and locate enemies within a region, finding their vehicles or some supply caches around might indicate that they either are, or have been, nearby. A siren alarm after players raid a base or attack a location is not an enemy attack in of itself, but it indicates that it is likely for reinforcements to come and respond to the threat.

This entails taking on a lot of assumptions about your players, and the above are very explicit examples. However, with proper thought, you can find your own ways of communicating with the players entirely through your mission alone, which the players may or may not catch.