An efficient digital signal is going to maximize the use of bandwidth if it looks like white noise. That said, a signal like that needs a carefully calibrated receiver, so part of the signal in time-frequency space is going to be allocated for something that is easy to acquire and will tell to how to decode the main signal. You might see a periodic structure: if you want to run a "signal frequency network" with multiple transmitters with the same signal, have to deal with a lot of reflected signals, or listen from a mobile terminal that suffers from the Doppler Effect you will probably turn off the signal for part of the cycle so that reflections can die down and you can reset your echo cancellation algorithms.
Thus digital signals aren't going to be invisible but they are going to spend maybe 5% of the energy in a way that is easy to interpret as opposed to all of it.
On top of that TV signals would have additional periodicity because the transmitters will be hidden behind the Earth once every 24 hours.