Distinguishing Jews Called for in Lateran IV: Canon 68 - On Jews
In some provinces a difference in dress distinguishes the Jews or Saracens from the Christians, but in certain others such a confusion has grown up that they cannot be distinguished by any difference. Thus it happens at times that through error Christians have relations with the women of Jews or Saracens, and Jews and Saracens with Christian women. Therefore, that they may not, under pretext of error of this sort, excuse themselves in the future for the excesses of such prohibited intercourse, we decree that such Jews and Saracens of both sexes in every Christian province and at all times shall be marked off in the eyes of the public from other peoples through the character of their dress. Particularly, since it may be read in the writings of Moses [Numbers 15:37-41], that this very law has been enjoined upon them.
Moreover, during the last three days before Easter and especially on Good Friday, they shall not go forth in public at all, for the reason that some of them on these very days, as we hear, do not blush to go forth better dressed and are not afraid to mock the Christians who maintain the memory of the most holy Passion by wearing signs of mourning.
This, however, we forbid most severely, that any one should presume at all to break forth in insult to the Redeemer. And since we ought not to ignore any insult to Him who blotted out our disgraceful deeds, we command that such impudent fellows be checked by the secular princes by imposing them proper punishment so that they shall not at all presume to blaspheme Him who was crucified for us.
From H. J. Schroeder, Disciplinary Decrees of the General Councils: Text, Translation and Commentary, (St. Louis: B. Herder, 1937). pp. 78-127.
Source: Medieval Sourcebook