Why do cranes have flags on them?

The short answer

Cranes fly flags to indicate wind conditions, display patriotism or remembrance, and comply with airport safety rules.

The long answer

Whether you're considered an ​umarell​ or not, you may have noticed before that flags are often flown on construction cranes.

Wikipedia defines umarells as "men of retirement age who spend their time watching construction sites, especially roadworks – stereotypically with hands clasped behind their back and offering unwanted advice to the workers."

"​Umarells​" by ​Wittylama​ is licensed under ​CC BY-SA 4.0​.

While the practice seems to be most common in the United States, flags can be found on cranes all over the world.

Here are three reasons why construction cranes fly flags:

Reason #1: Flags indicate wind direction and speed

First and foremost, flags serve a practical purpose. They let workers know the wind speed and direction, which can help improve workplace safety. If the crane is lifting something that could cause grease, dust, or debris to blow around, it's helpful to know where to stand to avoid getting hit.

As far as I can tell, there's no official requirement for cranes to have a flag, but it seems to be one of the tricks of the trade.

Reason #2: Flags display patriotism, corporate branding, union pride, or remembrance

While you could use a plain flag to indicate wind direction, it's an opportunity to display pride, advertise, or pay tribute to lives lost.

Cranes most often fly a national flag as a show of patriotism. Unionized workers may also fly a union flag to show pride. For all you ​football fans​, I also saw one flag hung in honor of the ​Liverpool Football Club​. Construction companies may use flags to fly their logo and take advantage of free advertising.

Flags can also be hung to honor those who have lost their lives during a construction accident. After a tragic tower crane accident in Seattle killed four people in 2019, a crane operator in Des Moines, who had served in the military with two of the deceased, flew American and U.S. Marine Corps flags in their memory.

Reason #3: Flags mark tall obstacles at airports

The only place where flags are mentioned in official regulations is in airport construction. Airports expand to add more terminals, but they're not going to ground all flights until the work is done. Instead, the ​International Civil Aviation Organization (ICAO) puts together a thick handbook​ on all the shared standards of how airports should be designed and run to maximize safety, which includes airport construction.

The ICAO requires all obstacles that could interfere with air traffic, such as a tall crane, are marked. While the rules mostly focus on specific paint designs, flags are listed as an alternative visual aid when paint isn't practical.

"​Crews Prepare Cranes For Discovery's Arrival (201204160001HQ)​" (modified) by NASA is part of the public domain.

Flags should be hung at the highest point, if possible, and must be at least 2 feet (0.6 meters) on each side. While no colors or designs are explicitly required for flags, it's common to see a checkered orange and white flag flown from cranes and other obstacles on the tarmac.

🧠 Bonus brain points

Why do they put trees on top of construction sites?

Flags aren't the only things you'll find on a crane. Construction sites will also often be seen with trees on top of buildings or cranes.

"​A crane against a blue sky​" by Pixabay is part of the public domain.

Placing a tree on top of a newly built structure is part of an ancient Scandinavian tradition called "topping out." When the last piece of steel is placed on the highest point of a building's structure, a tree is often attached. The tree is thought to symbolize good luck, show respect for Earth's natural resources, and celebrate the hard work of the construction crew.

Source: ​Designing Buildings Wiki​

As far as how and why these trees end up on cranes, information is sparse. According to ​Reddit​, trees may stay on cranes for good luck during the project, to symbolize no one died during construction, or to mark the "topping out" of the crane itself.

Christmas tree on top of a crane in Munich. Source: ​Reddit​

Trees may also end up on construction cranes to celebrate Christmas. Many cranes are topped with Christmas trees or even decorated with lights to celebrate the holiday. Redditors from Denmark, Germany, Canada, Norway, the U.S., Sweden, the U.K., and other countries have reported this very merry construction tradition.

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Sources

Australian Flag Makers. (n.d.). Crane Flags. Australian Flag Makers. https://www.australianflagmakers.com.au/products/crane-flags

Drawhorn, O. (2025, January 27). What Is a Topping Out Ceremony? All about the Scandinavian Tradition. Port of Seattle. https://www.portseattle.org/blog/what-topping-out-ceremony-all-about-scandinavian-tradition

Michael J. Perkins Elementary School. (2011, January 6). Ask the Experts: Why is a flag on the crane?. Michael J. Perkins School Blog. https://michaeljperkinsschool.blogspot.com/2011/01/ask-experts-why-is-flag-on-crane.html

Reddit. (2022, April 7). r/Construction on reddit: Does anyone here know why there is a tree on this crane?. Reddit. https://www.reddit.com/r/Construction/comments/tydj72/does_anyone_here_know_why_there_is_a_tree_on_this/

Triad Machinery. (2023, October 25). Federal Aviation Administration (FAA) Crane Guidelines for Cranes. Triad Machinery. https://triadmachinery.com/blog/federal-aviation-administration-faa-crane-guidelines-for-cranes

Wesley Homes. (2019, June 4). The Story Behind the Tower Crane Flags. Wesley Choice. https://wesleychoice.org/the-story-behind-the-tower-crane-flags/

Wright, M. (2016, December 22). The Tradition of Crane Christmas Trees. Astro Crane. https://www.astrocrane.com/the-tradition-of-crane-christmas-trees/