  We derive, in model independent way, the spin structure of the matrix element
for the reaction of associative $\Theta^+$ pentaquark production,
$\pi^{\pm}+D\to \Theta^+ +\Sigma^{\pm}, $ in the threshold region and in
collinear kinematics. The expressions for the polarization observables in this
reaction are found assuming spin 1/2 and different parities for $\Theta^+ .$ We
have proved that such reaction can be used for a model independent
determination of the P-parity of $\Theta^+$ only by measuring the $\Theta^+$
polarization. Other polarization observables, such as the dependence of the
$\Sigma^{\pm}$ polarization on the vector and tensor deuteron polarizations,
are insensitive to the $\Theta^+$ parity in the considered kinematical
conditions. All linear and quadratic relations between polarization observables
in $\pi^{\pm}+\vec D\to \Theta^+ +\vec\Sigma^{\pm}(\Theta^+ $ is unpolarized)
do not depend on the parity of the $\Theta^+$ pentaquark.
