In the advanced section it states:

n / N – Cycle through numberings. The options are:
none
show element numbering
show edge numbering
show vertex numbering

but in 2D vector data it states

n – Increase the displacement amount in 10% steps, wraps around from 100% to 0%

preventing the ability to look at numbering data. This is particularly problematic when debugging NC meshes and vector data on submeshes.

Edit: n / N also does not appear to work for a mesh loaded on its own.