Fragments of Suliban warp trails
A warp trail (also known as an ion trail) was a wake left by a starship using warp drive. A warp trail could be tracked with sensors, although there were ways of masking warp trails, such as traveling through a nebula.
In 2151, the Enterprise NX-01 followed a Suliban vessel into the atmosphere of a gas giant by tracking its warp trail. Enterprise did not originally have the sensor acuity to identify a warp trail, but this changed when Subcommander T'Pol modified the sensors to isolate the plasma decay rate of the Suliban ship. (ENT: "Broken Bow")
In 2153, Enterprise tracked the ion trail of an Osaarian vessel that had hidden inside a cloaking field to avoid detection. (ENT: "Anomaly")
In 2154, the crew of Enterprise pursued Doctor Arik Soong and his Augments into Klingon territory by tracking their warp trail. Once Soong discovered that Enterprise was using the Bird-of-Prey's warp trail to track them, he was able to successfully mask their warp trail. (ENT: "The Augments")
In 2356, Magnus and Erin Hansen attempted to mask their warp trail in a nebula when they and their daughter, Annika, attempted to escape from the Borg aboard the USS Raven. (VOY: "Dark Frontier")
In 2370, Chief Miles O'Brien was able to retrace a Maquis warp trail to find Gul Dukat. (DS9: "The Maquis, Part II")
In 2372, the crew of the USS Voyager discovered a warp trail leading away from a moon they had been surveying for polytheranide, which lead them to a seemingly lifeless planet with an unusual energy source. (VOY: "Tattoo")
In the same year, Voyager encountered the Cardassian Dreadnought missile in the Delta Quadrant. It contained a sophisticated array of computer technology as well as its own high-powered warp drive. To avoid detection, it was also capable of masking its own warp trail. (VOY: "Dreadnought")
A group of rogue Jem'Hadar used a magneton pulse to dissipate their ion trail after attacking Deep Space 9. (DS9: "To the Death")
In 2373, Benjamin Sisko told Worf to look for an ion trail generated by a runabout Kira Nerys had taken to interview several Cardassians suspected of being behind the killings of a number of former members of the Shakaar resistance cell. (DS9: "The Darkness and the Light")