Children are known for it. So are reporters. Both groups pepper people with questions. And a curious mindset can be useful, leading to an interesting conversation, or simply gathering information.
The question is, are your prospects more likely to read an interrogative yard sign than one that states what you're offering? It depends.
Just as with email and snail mail direct mailers, no one has divined the formula that works faultlessly every time — or all businesses would be using it. Businesses have tried all sorts of creative direct mail campaigns over the years, from eye-catching typefaces to unusual colors, odd envelope sizes to pseudo-friendliness (where the marketer purports to be an acquaintance of the prospect, sending along a sticky note attached to an article he's sure the prospect will want to read). Some approaches work some of the time, and others don't.