How To Subtly Indicate That Your Movie Is About A Father Seeking Revenge On The People Who Will Not Let His Daughter Go:
1. Have Liam Neeson stand in silhouette holding a gun. Nothing says, "I am a father seeking revenge on the people who won't let my daughter go, " better than a father in silhouette holding a gun (except maybe actual words saying that, but we'll get to that in a minute).
2. Black background. Darker colors = revenge movie, and the void surrounding Liam Neeson echoes his lack of information about the people who won't let his daughter go, without his having to actually come out and say, "I don't know who you are."
3. Write in giant font over the whole thing: "I don't know who you are but if you don't let my daughter go, I will find you. I will kill you."
Just looking at this poster, you know that the people who kidnapped Liam Neeson's daughter are really gonna get it—"it" here meaning "a super stern talking-to." And judging by the trailer, they could have gone a lot further with this poster:
"I don't know who you are but if you don't let my daughter go, I will find you. I will kill you. I will tear the Eiffel Tower down if I have to—which, let's face it, will probably be unnecessary unless you're planning on holding her hostage in some kind of bunker underneath one of the world's biggest tourist attractions—but I'll do it. Look, I know it's far-fetched. I just want you to know that I am prepared for any ridiculous scenario involving French landmarks if it means getting my daughter back and also killing you. I will tear up the Champs-Elysees with a bulldozer. The Arc De Triomphe will be the Pile De Bricks De Triomphe when I'm done with it. Just try me. My point is: if you don't give me my daughter, I'll pursue you so hard until--oh, can you hang on a sec, that's my call waiting—Sorry. Where was I? Oh right: I'll blow up the Louvre if it comes down to it. I've got a special set of skills, one of which is getting dynamite. Another one is holding my breath for a really long time. I can also remember the lyrics to any Prince & The NPG song, and even some songs by The Time. That's just a small sample of my skills. I will employ any and all of these skills against you. Point is: I'll kill you."
Obviously they would have had to use a much smaller font, but just think about how powerful it would have been to barely see Liam Neeson behind a giant block of text outlining his character's motivations.