Automatic modulation recognition (AMR) for some special phase shift keying (PSK) modulations, such as 8PSK versus π/4-differential quadrature reference PSK, or, quadrature PSK versus offset quadrature PSK, remains a challenge for practical applications, due to the same constellation shape. To address this issue, we shift our focus to the differences in coding schemes, which manifest themselves as fourth-order spectrum lines. Thus, the existence, position and amplitude of these lines are utilized as the robust features for AMR work. To alleviate the sampling burden, we also perform the proposed AMR algorithm with compressive measurements in the framework of compressive sensing.