Zen Faulkes (I wasn’t kidding when I said you should be following him) says no. In his post “Detective stories: ‘Whodunnit?’ versus ‘How’s he gonna prove it?’,” Faulkes argues that scientists’ curiosity leads us to overdo it on the questions.
Academic posters are meant to be understood in a flash. I’ve even heard the advice that people should be able to take in the gist of your project while walking by slowly without stopping. The best way to aid this rapid digestion is to “tell them the bottom line right away.”
I still think questions have their place in scientific communication. But if this blog post was the title of or a heading on an academic poster, I would format it: “You should not use questions on your posters” and include my supporting evidence to build that case.