The next step is to move the dish of the coordinates to see if the signal disappears. If it does not, then some disturbance must be causing it. But if it passes this test too, then it is established as a real candidate signal. The next step would be to examine the signal and decide whether it is truly artificial or merely some natural phenomenon. A good example of how tricky this could be is the dicovery of pulsars at Cambridge, England in the 1960s.
Pulsars are dead stars that rotate extremely fast, sometimes several hundred times a second.
For each rotation, they lash out a burst of electromagnetic radiation, which arrives at earth at very exact intervals. When such deep space regular bursts were detected at Cambridge, pulsars were not even known in theory, so it is easy to imagine how easily the signal by some people initially was mistaken for an artificial one. The source was even designated LGM, short for Little Green Men. Well, hopefully it would display some characteristics that clearly would distinguish it as artificial. Since mathematics would be the only universal language shared by all advanced civilizations, simple mathematical relationships should be the logical attention-getter of an intentional broadcast.