Sometimes signals are overt and quite clear, but often they are subtle and easy to miss.
Signals come in three varieties.
First there are those that people intend to send and that are true. People send signals instead of saying things outright in order to convey information while preserving some degree of deniability. Second, there are signals that people intend to send that are false. Third, there are signals that people unintentionally let slip out that can provide critical information on what they want or will accept. These unintended signals can be very valuable, provided that you can distinguish them from the misleading ones.