  Ambiguities of the signs of $N\to \Sigma K$ coupling constants are studied in
a multichannel partial wave analysis of a large body of pion and photo-induced
reactions. It is shown that the signs are not free from some ambiguities, and
further experimental data are needed. Data on the reactions $\pi^+p\to
\Sigma^+K^+$ and $\gamma p\to K^+\Sigma^0$ define rather well the isospin 3/2
contributions to these channels. However the lack of information on
polarization observables for the reactions $\pi^-p\to \Sigma^0K^0$, $\pi^-p\to
\Sigma^-K^+$ and $\gamma p\to K^0\Sigma^+$ does not allow us to fix uniquely
the signs of $N\to \Sigma K$ coupling constants. As a consequence, also the
contributions of nucleon resonances to these channels remain uncertain.
