  We investigate a signed version of the Hammersley process, a discrete process
on words related to a property of integer sequences called heapability (Byers
et al., ANALCO 2011). The specific version that we investigate corresponds to a
version of this property for signed sequences.
  We give a characterization of the words that can appear as images the signed
Hammersley process. In particular we show that the language of such words is
the intersection of two deterministic one-counter languages.
