Should I add references to a conference poster
This may be a somewhat discipline-dependent question (and you don't specify yours), but I can say that I have often seen references on posters -- and just about as often not. When I have seen them, they have generally been in the lower right-hand corner (for most left-to-right languages, the last place anyone generally looks). Not uncommonly they are in smaller type than the rest of the poster, to save space.