A Judas Goat is a goat used at slaughterhouses to lead cattle into the killing floor. They normally panic at the smell of blood but seeing an animal that is used to it and not reacting in fear calms them into believing that whatever awaits them in that room won't be all that bad. They find out only after they're trapped and the killing begins.
When Billy Russo tries to contact Frank Castle by broadcasting "Raven (Frank's call sign), this is Blackbird". Raven was Rambo's call sign used by Col. Trautman to contact Rambo when trying to convince him to surrender in the movie, First Blood (1982).