Serpentinization is a geological process involving the interaction of water and ultramafic rock, the chemical byproducts of which can serve as an energy source for microbial communities. Although serpentinite systems are known to host active microbial life, it is unclear to what extent fossil evidence of these communities may be preserved over time. Here we report the detection of biosignatures preserved in a mineralized fracture within drill cores from the Samail Ophiolite in Oman. Two varieties of filamentous structures were identified in association with iron oxide precipitates. The first type are interpreted as likely microbial remains, while the second type are recognized as potentially microbiological dubiofossils. Additionally, laminated structures composed of carbon and nitrogen rich material were identified and interpreted as having a microbially-associated origin. Our observations affirm the potential to detect subsurface microbial communities within serpentinizing environments and highlight a unique taphonomic window to preserve evidence of rock-hosted life.