From documents found at The YIVO Institute for Jewish Research in New York ~ see below : the family name in Yiddish was spelt in such a way that it was pronounced: Lubavitsch ~ . the first document below (YIVO number 24742-2) from the Committee of Jewish Community of Mazeikiai (Vaad ha’Kehila), early 1920’s, bears the names of Berre, Hene-Leah and Mirjasha with a signature; the second document below (YIVO number 24743-2) bears the name and signature of Berre’s daughter, Tzire Poliakov, aged 22, maiden name Lubavitsch

(click to enlarge : names of Berre & fam. on the left, second from bottom)

(click to enlarge : Tzire Poliakov's name and signature on the left, top row)