First of all, sorry for the general context of the question but I’m very inexperienced. I hope I'm not breaking the rules.
Simplifying, in the short sci-fi novel I’m writing there’s a super-intelligent alien probe that wants to communicate with us. She can intercept all of our communications leaving the Earth so she chooses to send a signal to the ESTRACK (or one of the other deep space networks).
Let’s say that the probe wants to send a simple “text” message, maybe a “do you copy?” if she’s starting to learn english, to grease us the wheels. How she can do it? Which kind of... “format” the signal should have to be received and understood?