Is there a universal symbol for a problem?
I ask that question in all seriousness. Although, this post uses a question mark ("?") as the thumbnail image, I really do not think that a question mark is a good universal symbol to represent a problem. I do not think a question is automatically the same thing as a problem, even though finding a solution to a problem requires you to ask many questions.
Maybe a good symbol would be the classic "round peg and square hole" that don't seem to fit to each other. Most people would recognize those as being a problem, but maybe not representing all problems.
This is a serious question to me. Some folks like the existing cover of The Dog Barks When The Phone Rings: An Engineer's Guide to Solving Problems and some folks just scratch their heads and ask, "what's that picture about?"
We could use a cover image of a tool. Maybe something like a hammer and nails. But tools and toolmaking represent a single chapter, so it doesn't really make sense to put all of the focus there.
A popular TV sitcom once showed two physicists staring at a whiteboard, while dramatic music filled the soundtrack. The conflict between such static people compared to such dynamic music created a lot of laughter. But the point is valid: it is difficult to portray people thinking. So much of problem solving is scribbling little drawings and talking to ourselves and each other while we work through a problem. Not exactly the dynamic images of something like sports.
So what do you think? Is there a (simple) universal symbol for a problem?