It’s a scene you’ve seen countless times in movies: two strangers meet on a park bench; one hands over an envelope full of confidential information; the other hands over a briefcase. Inside that briefcase are stacks and stacks of crisp bills.

It certainly makes for great cinema, but it’s unlikely the money you see on screen is real. When it comes to producing money solely designed for film, prop makers are very good at it. In fact between 1970 and 2000, prop houses made more than 250 types and 2,000 sub-types of movie money.

The reason movie-goers don’t see real bills on screen is because there’s too much liability involved when it comes to the real stuff. Think of all the movies you’ve seen where thousands of bills are destroyed in an explosion. That’s where prop makers are tasked with finding ways to customize prop movie money, making bills that are similar enough to the real thing. If a film does require the burning of money, filmmakers have to use prop money under 18 USC 333, which bans currency mutilation or burning.

For many counterfeiters, the prospect of being able to customize prop movie money is tempting, but the United States government has come up with quite the deterrent. Anyone trying to use prop money to make purchases may face fines of up to $250,000 and up to 20 years in prison.

While prop makers all over work on ways to customize prop movie money, you the movie-goer are probably wondering how to tell the difference between real money and prop money. Here’s what you need to know:

• Watermarks: All of the real United States currency you’re carrying in your pocket right now has a distinguishing watermark. If you hold a $100 bill up to light for example, Ben Franklin appears on the far right side, no matter which side of the bill you’re looking at. If that doesn’t happen, it’s not a real bill. In fact, one way that prop makers customize prop movie money is by leaving blank the spot where the watermark is supposed to go.
• Ink: Another way to tell the difference between real and prop money is the colors of the ink. On a real $100 bill, the ink used to print the 100 on the bottom right corner shifts in light. If you hold it up to light and look there, you’ll notice the ink changes from copper to green. Another way to verify authenticity is to touch the bill. If it’s real, you’ll be able to feel the slightly raised ink.
• Security: If you’ve got real money in your hand, you’ll be able to see a security thread that runs vertically down bills of $5 and higher. When you hold it up to light, you’ll be able to see the thread and it should glow a different color when held under UV lights. Prop money doesn’t include a security thread.

Scenes involving money film props in movies look pretty cool on the big screen, but prop money should be kept where it belongs: in the movies. Knowing how to spot differences between real currency and prop money will make it easier for you to avoid getting swindled by counterfeiters.