It is therefore preferable to act in the following manner: After nightfall (3 stars coming out), before one leaves his house, each person says "Baruch Ha-Mavdil Bein Kodesh Le-Chol" and puts on his Tisha Be-Av shoes (and see Shut Yechaveh Daat 5:38). In order to do so, Maariv should be delayed 15 minutes. If one is unable to act in this manner, he should put on his Tisha Be-Av shoes at home on Shabbat and walk to Shul in them so he is not preparing on Shabbat for a weekday, since he is using them on Shabbat itself. Even though this seems to contradict the concept of not displaying signs of mourning on Shabbat, our Sages allow one to wear regular shoes on Tisha Be-Av if one is traveling or if one lives among non-Jews and he fears being mocked (Shulchan Aruch, Orach Chaim 554:17), and the same leniency applies for the honor of Shabbat and he may wear his Tisha Be-Av shoes on Shabbat.