In this paper, a novel scheme of reconfigurable intelligent surface (RIS) aided index modulation (IM) for orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems is proposed, where the RIS acts both as a passive reflecting surface and an additional information source. In the signal detection module, a low-complexity deep detection network based on signal energy is designed for RIS-IM signals and OFDM-IM signals. A theoretical analysis of the bit error rate (BER) is performed for the proposed algorithm, based on which two RIS coding schemes are given. Simulation results show that the proposed detection algorithm performs well under both frequency-selective (FS) fading and flat-fading channels. The proposed scheme that introduces RIS indices can transmit additional information while improving the transmission performance of OFDM-IM signals, and the two provided RIS coding schemes provide considerable performance gains for each of the two signal types.