Plasma wake
A plasma wake was the trail of ionized nebular gases left behind by powerful warp engines of starships traveling inside a nebula.

The Jem'Hadar were able to detect the cloaked  while it traveled through the Badlands in 2373 by homing in on its plasma wake. Jadzia Dax compared it to a Ligorian mastodon moving through the forest – "you may not be able to see it, but it definitely makes the leaves rustle."  ()

See also 
 Ion trail

Warp
Subspace