  A generalised Thurston-Bennequin invariant for a Q-singularity of a real
algebraic variety is defined as a linking form on the homologies of the real
link of the singularity. The main goal of this paper is to present a method to
calculate the linking form in terms of the very good resolution graph of a real
normal unibranch surface singularity. For such singularities, the value of the
linking form is the Thurston-Bennequin number of the real link of the
singularity. As a special case of unibranch surface singularities, the
behaviour of the linking form is investigated on the Brieskorn double points
x^m+y^n\pm z^2=0.
