Invisible Cows and a 17.3 MPH Speed Limit? 4 of America's Strangest Road Signs

America's roads are covered with familiar signs telling drivers when to slow down, yield, or watch for wildlife. Most blend into the background after years behind the wheel. A few, however, are strange enough to make drivers stop and take a second look.

From a warning about supposedly invisible cows in Hawaii to a highway associated with UFO sightings in Nevada, these four signs stand out for their unusual wording, unexpected speed limit, and stories behind them.

Beware of Invisible Cows — Hawaii

Wildlife warning signs are common across the country. Drivers regularly encounter signs for deer, horses, and other animals that might wander onto the road. But a warning about invisible cows is a different matter.

Near Hawaii's Mauna Kea volcano, one unusual sign tells motorists to watch out for animals they seemingly cannot see.

The explanation is less mysterious than the wording suggests. The cows aren't actually invisible. Their dark coats can make them difficult to spot when fog rolls in and visibility drops. Much of the surrounding area is open-range land, allowing cattle to roam freely and occasionally cross roads.

The warning serves a practical purpose: drivers should slow down and watch carefully for cattle that might emerge from the fog with little warning. Ignore the sign, and an encounter with an almost invisible cow could leave a lasting impression on your vehicle's hood.

A Speed Limit of 17.3 MPH — Wisconsin

Speed limit signs usually feature familiar numbers such as 15, 20, or 25 mph. One sign near the Outagamie County Recycling and Solid Waste facility in Appleton, Wisconsin, takes a rather different approach.

The posted limit is 17.3 mph.

That unusually precise figure might look like a mistake, but the facility has explained the reasoning behind it. In a Facebook post, Outagamie County Recycling and Solid Waste pointed out that the unusual number is meant to catch people's attention.

The site sees a steady flow of waste haulers, contractors, and local residents. With so much activity, keeping drivers alert is an important part of maintaining safety.

"We have haulers, contractors, and residents moving through our site every day. With so much activity, staying alert is key to keeping everyone safe," they wrote.

Rather than letting drivers automatically follow a familiar speed limit, the unusual number encourages them to pay closer attention to their speed and surroundings.

"End of the Earth, Porcupine Mountains" — Michigan

Road signs generally tell drivers where they're going, but one sign in Michigan's Upper Peninsula makes the destination sound considerably more dramatic.

Near the Porkies Outpost restaurant, motorists can find a sign reading "End of the Earth, Porcupine Mountains." The wording alone is enough to make anyone do a double take.

The distances make the sign even more intriguing. The so-called end of the Earth is listed just 2 miles away, while the Porcupine Mountains are 4 miles ahead.

There's no geographical mystery to solve. The wording plays on the area's remote character and the sense of isolation visitors may experience there.

The Porcupine Mountains have relatively few roads running through them, and Porcupine Mountains Wilderness State Park covers approximately 60,000 acres. With so much wilderness surrounding visitors, the landscape can feel like the edge of the known world.

The sign's dramatic message is an exaggeration, but its setting helps explain why the joke works.

The Extraterrestrial Highway — Nevada

Nevada has a road sign that seems tailor-made for anyone fascinated by UFOs and extraterrestrial mysteries.

Near the communities of Rachel and Crystal Springs, signs identify Nevada State Route 375 as the Extraterrestrial Highway. The designation has turned a remote stretch of desert road into a destination for travelers hoping to catch a glimpse of something unusual in the sky.

The highway's reputation is closely tied to Area 51, the military installation that has long occupied a prominent place in UFO culture. Stories about alien encounters, mysterious aircraft, and alleged extraterrestrial technology have helped fuel the fascination.

Reports of strange sightings along the highway have added to its legendary status. Local authorities eventually embraced the area's association with UFO lore, and the unusual road signs became part of the attraction.

The first sign appeared in 1996. Since then, it has repeatedly been stolen or vandalized, earning a reputation as one of Nevada's most frequently stolen road signs.

For a highway cutting through an otherwise remote desert landscape, its extraterrestrial identity has made it anything but an ordinary drive.