<>No training or SOP would tell officers to shoot a round into the ground to alert other officers to something. That's what radios are for. But, the real question is why wasn't the operations center relaying messaging from the local LE to the USSS guys. Hopefully it is all recorded and released at some point.
FYI, we keep hearing the radios weren’t on the same frequency; or, otherwise weren’t working. It was an unpredicted situation, not anticipated or prepared for.