Under Siege 2: Dark Territory (1995)
'A top secret nuclear satellite. A team of international terrorists. A government held hostage. An undetectable moving headquarters. Only one hero stands in the way.'

This movie, I surmise, has the exact same plot as the first Under Siege except it takes place on a train instead of a boat. The poster deviates from the formula a little in that there are actually other people on it though Seagal is of course the largest and most prominent. He's also on it three times. Two of those holding a gun. Overkill perhaps, but I think it's a nice variation on the theme. And hey, he must be a badass if he can cling to the side of a fast moving and on fire train with only one hand and that same devoid of any emotion look he has... all the time. Also notice that the subtitle of the movie follows the two-word title rule.