  A general discussion is made concerning the ways in which one can get
signatures about a possible liquid-gas phase transition in nuclear matter.
Microcanonical temperature, heat capacity and second order derivative of the
entropy versus energy formulas have been deduced in a general case. These
formulas are {\em exact}, simply applicable and do not depend on any model
assumption. Therefore, they are suitable to be applied on experimental data.
The formulas are tested in various situations. It is evidenced that when the
freeze-out constraint is of fluctuating volume type the deduced (heat capacity
and second order derivative of the entropy versus energy) formulas will prompt
the spinodal region through specific signals. Finally, the same microcanonical
formulas are deduced for the case when an incomplete number of fragments per
event are available. These formulas could overcome the freeze-out backtracking
deficiencies.
