I put the engine on the tracks, power up, and throttle up. If it runs long hood forward, I figure it was meant to. However, many of the better models do have the F to indicate the front.
The Lionel PRR GP7 and Trainmaster are long hood forward, but the reading GP7 and GP7 as well as their Trainmaster are short hood forward. The giant clue, other then the F, is the engineer is also facing that way.