There are some places where you expect to see a warning sign. Then there are places where you come across one and immediately wonder what possessed someone to put it there. A few words on a piece of paper can turn an otherwise ordinary location into somewhere that suddenly feels like it has a story.

The creepiest signs are often the ones that give you just enough information to become concerned without actually explaining anything.

A warning about something you had never considered dangerous, an oddly specific instruction or a message that sounds like it was written after a very bad experience can leave you with more questions than answers.

Some are frightening because of what they describe. Others are unsettling simply because of where they appear. And then there are the signs that are technically harmless but somehow manage to make the entire situation feel much worse.

It is hard not to imagine what happened before these signs were installed. There may be a perfectly reasonable explanation for all of them, but when you encounter a particularly ominous warning with no context, your imagination tends to fill in the gaps.

These 21 signs are the kind that make you pause, read them again, and wonder whether you should really keep going.