Ever get handed a big bill and feel a tiny knot in your stomach? Same. I work the register at a small coffee shop. I also sell granola at the Saturday market. Cash comes fast. Smiles are nice. But a bad bill can ruin your day.
If you're curious about the blow-by-blow of my very first week experimenting with the marker, I've laid it all out in detail in this field test.
So I bought two brands of counterfeit pens: Dri Mark and Sharpie Counterfeit Detector. I kept one at the shop and one in my market apron. I’ve used both for months. Here’s what I learned, the easy way and the hard way.
What Is This Pen, really?
It looks like a normal marker. The tip is a pale yellow. You make a small mark on the bill. Then you watch the color change. That’s it.
- Light yellow or almost clear: likely real
- Dark brown or black: likely fake
Simple, right? It felt like a magic trick at first. But it’s not magic. It’s paper science.
How It Works (Plain Talk)
Real U.S. money isn’t wood-pulp paper. It’s cotton and linen. Like clothes. Fake bills are often wood pulp, which has starch. The pen ink has iodine. Iodine meets starch and turns dark. No starch? The mark stays pale.
So the pen isn’t “reading” the ink on the bill. It’s checking the paper.
That one detail matters a lot.
Real-Life Moments That Stuck With Me
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Coffee shop rush, Tuesday morning: A man handed me a crisp $20. I marked it near the portrait. It flashed dark brown in seconds. My gut dropped. I asked for another form of pay. He didn’t argue. He just left. I kept the bill in an envelope for the manager. That pen saved us right there.
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Saturday market, windy day: A woman paid with three $10s. All used and a bit soft from the wash. The pen mark stayed light yellow. I still checked the watermark by holding it to the light. I saw the little face and the strip. Sold her granola and said thanks. The combo check made me feel safe.
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PTA bake sale, rainy spring night: A teen gave me a damp $50. My pen streak turned a weird gray. Not brown, not yellow. My heart sped up. I waited a minute, tried a fresh spot after it dried. It stayed pale yellow that time. We also checked the security strip. It looked good. We took it. Moisture can make the mark look odd. Lesson learned.
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Yard sale with my kids: We used the pen on a $100 from a neighbor I know well. Pale yellow. We still looked for the color-shift “100” by tilting the bill. It changed from green to copper. My son said, “Whoa, it’s like a mood ring.” Not wrong, buddy.
The Good Stuff
- Fast: One second, tops.
- Cheap: I paid about $6 for a single pen; a three-pack was under $15.
- Easy: Mark the bill in a blank spot. I like the white margin or a light area on the back.
Both pens worked the same for me. The Dri Mark cap fit tighter, which I liked. The Sharpie one felt smoother on old bills. Small difference, but I noticed.
The Not-So-Great Stuff
Here’s the thing. The pen checks the paper type. Smart crooks can bleach a real $1 and print a fake $20 on it. That paper is still cotton. The pen might say “looks fine,” even though the print is wrong. Also:
- Wet or coated bills can confuse the ink.
- Super old bills with grime can test weird.
- It doesn’t check watermarks, strips, or color-shift ink.
Those gaps are exactly why I spent an evening comparing pro tips online, and the clearest breakdown I found lives on Pretty Fakes, where you can see real vs. counterfeit bills side-by-side. That rabbit hole pushed me to document the exact setup I carry every day, which you can read in my guide to spotting fake bills and the gear that actually works.
For a full, official rundown of every security feature—from micro-printing to color-shifting ink—the U.S. Currency Education Program hosts free charts, high-resolution images, and printable training materials.
So no, the pen isn’t a shield. It’s more like a quick sniff test.
How I Use It Now (My Routine)
When I get a $20 or higher, I do three fast checks:
- Pen mark: pale yellow means likely good.
- Hold to light: look for the watermark face and the thin security strip with tiny letters.
- Tilt the bill: see if the number shifts color.
This takes maybe five seconds. If you want a quick visual refresher, the Federal Reserve’s classroom video assignment, “How to Authenticate U.S. Currency,” walks through the exact same steps.
If anything feels off, I ask for a different bill or another way to pay. I stay calm and kind. Most people understand.
Tips I Wish Someone Told Me
- Mark a small spot. Don’t scribble across the face. It’s money, not homework.
- Keep the cap tight. These dry out fast.
- Replace every year. The ink fades over time.
- Don’t test on wet bills. Let them dry first.
- If the mark is dark, don’t hand the bill back. Follow your store policy and call a manager.
Who Should Keep One?
- Cashiers, baristas, and food truck folks
- Market sellers and craft booth owners
- Yard sale hosts
- School clubs and church events that take cash
Speaking of quick, real-world exchanges, if your off-hours plans ever involve lining up a spontaneous drink date you just set up through PlanCulFacile—the platform’s streamlined sign-up and smart location filters help adults arrange discreet, no-strings meet-ups in minutes—you’ll be glad to have a pen handy for any cash the two of you swap for cover charges or late-night tacos. And if you’re scrolling local classifieds for nightlife-friendly connections in the San Gabriel Valley, the curated listings on Backpage Diamond Bar showcase up-to-date ads and safety tips that can help you vet meet-ups before you ever leave the house.
If your business also has to check IDs—think bars, festivals, or late-night events—you might like seeing what happened when I tested the most popular counterfeit ID detectors.
Honestly, even my babysitter keeps one for late-night pizza runs when friends chip in cash. Sounds extra, but it helps.
Final Take
Do I trust my counterfeit bill pen? Yes—and no. It’s quick and cheap. It’s caught at least one fake for me, and it warned me during that rainy-night weird mark. But I never rely on it alone. I pair it with the watermark, the strip, and the color-shift check.
You know what? That mix feels right. The pen is my first look. My eyes are the second. Together, they’ve kept my till safe, my line moving, and my stomach knot-free. And that’s worth way more than six bucks.