Family in general: "The Noble and Most Ancient House of Black" ; Sirius' parents were convinced that to be a 'Black' made you "practically royal."
Family crest is mentioned in OP but not described; however, Rowling drew it on her Black Family Tree. It shows a shield with greyhounds rampant charged with a chevron, 2 five-pointed stars and a short sword. In the formal language of heraldry, it is: "Sable, a chevron between two mullets in chief and a sword in base, argent." (Thanks to Richard for the terminology).
Family motto: Toujours pur ("always pure" in French) (from tapestry in OP6 and BFT).
Tapestry: a tapestry exists at number twelve Grimmauld Place that has, according to Kreacher, been in the family for seven centuries (OP). On it the family's births, marriages and deaths are embroidered with gold thread; family members who have been disowned have been "blasted" from the fabric (a small burn like a cigarette burn is where their name is).
Important sources of information on the Black family: OP where we meet the portrait of Sirius' mother; OP where Sirius explains the Black family tapestry to Harry, and the Black Family Tree, a hand-drawn tree that Rowling donated to Book Aid International in January of 2006.