Extraterrestrial intelligence may be slow
One way they can get our attention is to create an infectious and more fatal-than-normal virus and set it loose. A single virus would self replicate and spread. The numbers of infected and the severity of their outcomes would definitely get the attention of the leaders. Watching from afar, they would see who is actually in control, and more specifically who is most productive to interact with. The message may be encoded cleverly in the statistical variations of outcomes among different sub-populations.