What does the signals in a XPS spectrum mean?
you are quite right, XPS does measure the 'binding energy' of electrons. More specifically, XPS bombards a surface with X-rays and when those X-rays have sufficient energy they are able to sufficiently excite electrons to be emitted from the sample. Each peak in an XPS spectrum corresponds to the energy necessary to emit a given electron.

So what would you expect to see for Mo?


Outer lying electrons (for Mo, we are talking about electrons in the
4p and 4s orbitals) will emit at a lower energy. You should observe
low-energy peaks that correspond to these emissions (approx. 30 - 60
eV).  
you should see a cluster of peaks at approx. 230 eV that correspond to the d-orbital electrons.
Finally, you might see discrete peaks at very high energy, approx. 2600 - 2800 eV that    correspond to emission from the 2s and 2p orbitals


In general, outer orbitals emit at lower energy, and inner orbitals emit at higher energy. 

Hope this helps!