We know irony when we see it. These unexpected moments often catch us by surprise and get stuck in our heads by completely contradicting our expectations. "In situational irony, there is a clash between the professed or ostensible aim of some person or entity, and the situation that they’re in," philosophy professor Mitchell Green, author of Irony as Expression (of a Sense of the Absurd), explained to Bored Panda.

According to him, witnessing a house burning down is tragic, though not ironic. "But when a firehouse burns to the ground, that’s both tragic and ironic, and in particular is a case of situational irony. The reason is that firehouses are built for the purpose of helping to prevent fires. That purpose is dramatically foiled by the firehouse burning to the ground."

"Similarly, when the president of the local chapter of Mothers Against Drunk Driving gets pulled over by the police and arrested for Driving While Intoxicated, we have a case of situational irony," Green continued. "Her professed aim is to campaign against drunk driving, but it’s upended by the outcome of getting pulled over on a DWI." He added that we also take some schadenfreude-based pleasure (that we get from witnessing someone's misfortune) in seeing this person shown to be such a hypocrite.

The philosophy professor pointed out that situational irony is different from what is often called verbal irony. "In verbal irony, a person is attempting to communicate that some situation she has in mind is ironic or absurd. (I say, 'Nice job' in response to your backing up your car into a tree, for instance.) But a situation can be ironic without anyone commenting on it."

But even though we instinctively understand when a situation is ironic, we often have trouble defining and articulating the term. Professor Green told us it can be hard to put into words and express what is needed for an incident to be ironic because these situations are complex while their features don’t always register at the conscious level. "This is similar to the way in which we can often tell whether someone is lying to us but we can’t say exactly what leads us to think that. In our social lives, we often respond to complex cues without attending to all the factors that guide that response. This may be why it’s hard to explain in words what irony is," he noted.

As you're scrolling through this compilation of pictures, you'll notice that some signs look more absurd than ironic. They make us stop, take a second to think, and quietly whisper, "What on Earth is going on here?" There’s no doubt that illogical and out-of-context messages make us slightly baffled, yet they are also a perfect source of entertainment.

Green told us that he sees irony as a form of absurdity. However, lots of things are absurd without being ironic, he added. "A chihuahua barking ferociously at a Great Dane is absurd, but it’s not ironic because the chihuahua doesn’t profess to intimidate the Great Dane. (He’s just trying to.) And of course, if the existentialists are right, maybe life itself is absurd. But that doesn’t mean life is ironic."

This does beg the question, why do so many of us feel amused when coming across these ludicrous announcements? "I suspect there’s a bit of schadenfreude in people’s enjoyment of these signs," the professor noted. "Not only do we enjoy the situational irony, but we also take a bit of pleasure in seeing the institutions that placed the signs coming across as foolish. This is of a piece with the more general fact that we love it when powerful institutions show their weaknesses, just as when famous people do." And what we enjoy even more is snapping a photo and showing our discoveries to everyone online. So if you have the perfect picture stored in your gallery, don't be shy and share it with us in the comments!