  The present paper deals with some characterizations of rectifying and
osculating curves on a smooth surface with respect to the reference frame
$\{\vec{T},\ \vec{N},\ \vec{T}\times\vec{N}\}$. We have computed the components
of position vectors of rectifying and osculating curves along $\vec{T},\
\vec{N},\ \vec{T}\times\vec{N}$ and then investigated their invariancy under
isometry of surfaces, and it is shown that they are invariant iff either the
normal curvature of the curve is invariant or the position vector of the curve
is in the direction of the tangent vector to the curve.
