Hint: If if $A\in O_n$ then $A^{-1}=A^T$. So if $M$ is symmetric or anti-symmetric, what does that say about the relationship between $A^{-1}MA$ and $(A^{-1}MA)^T$?
Hint: If if $A\in O_n$ then $A^{-1}=A^T$. So if $M$ is symmetric or anti-symmetric, what does that say about the relationship between $A^{-1}MA$ and $(A^{-1}MA)^T$?