Beyond telling anyone.
Also, signals such as described are practically useless in coordination.
To illustrate that, assume you are an operative. You are told where to go to attack what. And you are told what your signal will be.
To utilize the signal, all the information (and alternatives) have to be relayed to you in advance. That's a LOT of information that has to be SECURELY transmitted to you just so you can use the cute like AK-47 icon on the web page.
Not to mention the ease of locating anyone accessing that website.
This reads more like someone's spy fantasy rather than reality.