As usual, more context might help to clarify this excerpt but I understand here t’annoncer to mean announcing your presence, i.e. declaring publicly who you are and indeed draw attention before or by knocking to the doors of the city. This latter part is open to speculation depending on whether the person is outside or inside that city.

In the former case, that might mean the narrator advise the person to stay discreet and enter the city unnoticed, without “knocking the door”, but let that person decide to act differently and enter the city an ostentatious way should (s)he prefers to.

In this context It means That you announce your presence. You let everyone know you’re somewhere. You want to get the attention.