Some geometric structures of wave equations on manifolds of `neutral   signatures'
  In this paper, we study the symmetries and perform other geometric analyses of the wave equation on some spacetimes {with non diagonal metric $g_{ij}$ which are of neutral signatures}. Wave equations on the standard Lorentzian manifolds have been done but not on the manifolds from metrics of neutral signatures. 
Jean-Juste Bashingwa and A. H. Kara
math-ph math.MP