Orthogonal frequency division multiplexing (OFDM) is widely considered as a promising technique for vehicular communications. In current OFDM-based vehicular communications systems, a portion of tones are dedicated for pilot symbols and transmitted along with the data-bearing tones to estimate residual frequency error. However, these pilot symbols themselves do not carry any information, thus inevitably degrading the system spectral efficiency (SE). Motivated by the concept of index modulation (IM), in this paper, we propose a novel pilot insertion technique to enhance the SE, in which the pilot positions are selected according to extra information bits. Specifically, two different types of pilot position selection (PPS) schemes, which result in equal-spaced and unequal-spaced, are studied, and the corresponding pilot position detection (PPD) methods are designed. Computer simulation results corroborate the advantages of the proposed technique in terms of bit error rate (BER).