Signed differential posets and sign-imbalance
  We study signed differential posets, a signed version of differential posets. These posets satisfy enumerative identities which are signed analogues of those satisfied by differential posets. Our main motivations are the sign-imbalance identities for partition shapes originally conjectured by Stanley, now proven by Lam, Reifergerste and Sjostrand. We show that these identities result from a signed differential poset structure on Young's lattice, and explain similar identities for Fibonacci shapes. 
Thomas Lam