It's M4V, not M0V.
In principle, spectral classes can be further subdivided, particularly in the M class, because there are significant differences between an M4 and an M5 spectrum for instance.
Therefore you may see spectral classifications of M4.0 or M4.5 for instance (and even finer subdivisions are occasionally quoted).
The difference between M4 and M4.0 is the implication that the spectral class has been determined more precisely for the latter.
The V just means it is a dwarf. This can also be judged from the spectrum and is therefore part of a full spectral classification.