Lets consider wireless signals. The signals themselves travel in all directions, so there is no specificity. The frequency provides the sender-receiver specificity. The signal pattern contains information that the receiver can decode, i.e. the receiver must expect a specific type of pattern.
Comparing the general idea to biological signaling... the specificity usually comes from binding affinity, so that aspect of signaling is clear. Now for decoding the information. A pathway probably has multiple molecules serving as signal carriers. The pattern of concentrations of those input molecules *might* serve as the encoded information that the receiver, i.e. the pathway, is able to decode. The pathway then sends a new set of molecules as output signals . Note that this results in a conversion of signal carrier, which is analogous to the wireless signaling analogy where the wireless signal is decoded into some other form such as digital signals.