yytz: Shulchan Aruch YD 265:4 – “We publicize at the time of the Bris Milah that the baby is a mamzer.” The Shach there says that mamzerim are not given a Bris Mila inside the shul like kosher children are, but outside the shul. The Gra quotes the source for publicizing that the baby is a mamzer by the Bris is a Gemora in Yevomes 78b. The Gemorah there says that a Rov publicized the fact that a somebody was a mamzer. The person came to the Rov to complain and the Rov said that if I had not publicized this, you would have died.
Rema YD 265:4 – “???????? ???? ????? ???? ????”