In West Virginia, a purple stripe means "no trespassing," so if you see one, don't cross it.
In 61-3B-1 of the West Virginia State Code, trespassing is illegal on "Posted land" marked with "a clearly visible purple painted marking."
The law states that the purple marking must be "one vertical line no less than eight inches in length and two inches in width,
and the bottom of the mark not less than three nor more than six feet from the ground or normal water surface"
The purple mark does not replace traditional no trespassing signs, which must be placed "at all roads, driveways, or gates of entry onto the posted land"
If you encounter a property line away from roads, driveways, or gates, you may not see signs.