These memes are really effing weird, but sometimes weird is good. Not everything in life has to make complete sense - especially stock photos, like who comes up with that crap and who uses it? Sometimes it's just better to not question these things and enjoy the bizarre humor - our world can only take so much rationality.
The warning signs here are doing a great job. Like if you find yourself about to swim and then notice a little ol' ENORMOUS SIGN in all caps that says "THIS RIVER IS CONTAMINATED WITH FECAL BACTERIA" you may find yourself a little dissuaded from jumping in. So good job, terrifying signs of the world. Some of these signs don't even know they're scary, sinister or weird, but that doesn't make them not have a threatening aura.