If your talking about a opposite tack thing. watch the background. I sail mostly on lakes so this is pretty easy. I think the old saying is if the other boat is eating the trees in the background they'll cross you, if you see new trees emerging from the jib of the other boat you'll cross them.

Something like that ....

Seems like when I had my H-20 I would look forthe mark to be just past the beam to tack for it. Of course that's when the header shows up.