The next time you check your bags, pay particular attention to the three-letter code the counter agent puts on those bag tags.

MAD does not mean Madison, Wisconsin. It means Madrid.

LON is not London’s Heathrow.

Pay even closer attention if your bags are connecting to a second or third flight.

Make sure the final destination’s correct three-letter code is visible.

Recently in Singapore, a supposedly angry baggage handler swapped hundreds of baggage tags and then reapplied them to other bags, sending them to the wrong destinations.

That was an intentional crime.

But in most cases, it’s still your responsibility to look at those tags and make sure the three-letter city code matches your destination.

By the way, not all three-letter codes are helpful.

They can be misleading—so get to know them.

What if your bag tag says FAT? It’s one of the older three-letter codes.

You’re going—or at least your bag is going—to Fresno, California.

For more information about air travel and luggage, check out:

• How Ugly Suitcases Can Make Traveling Easier
• One Way You Can Track Your Checked Luggage
• Tips for Checking Your Luggage Through Multiple Flights

Keep reading for more travel tips.