A hiking trial? Sounds like a grueling hike. This caption was in the Fredericksburg, Virginia, Free Lance–Star on Feb. 23, 2017.
Don’t let this happen to you: Maintain a list of “bad words”—words that probably shouldn’t be in your documents but that a spellchecker won’t catch. Search for these words as part of copyediting. Trail happens to be in my own list but in reverse: that is, trial is more likely to appear in the work I edit, and trail is more likely to be a typo.