You might see them near freeway exits, at the corner of intersections or on the side of streets: little yellow signs with black lettering and an arrow.

These signs are put up by production companies filming all around Atlanta.

But if you’ve paid attention to what’s written on these signs, you’ll know that they don’t just say the name of the movie or TV show being filmed. Instead, they’ll have some seemingly unrelated word or collection of letters and numbers.

This is code, and WABE wanted to know how to crack it. So we enlisted the help of an expert ─ Matt Walljasper, who covers what’s filming locally for Atlanta Magazine.

Here are a few tips from Walljasper:

Know what’s filming in Atlanta. Sometimes the code can be as simple as an abbreviation or acronym. For example, the signs for “Alvin and The Chipmunks 4” have “AC4” printed on them. Similarly, production signs for a NBC show called “Game of Silence” feature just “GOS.”

Learn a little about the production companies working in Atlanta. Take the sign you see in the photo above. That sign is for a TV pilot called “Cordon.” Walljasper says “1159” is actually the address for Bonanza Productions, the company producing the pilot. Another example: When the “Walking Dead” was filming in Atlanta, its production company Stalwart Films used signs that said “SF.”

In cases where neither of those rules work, Walljasper says you’ll have to be more patient. Films that are likely to attract crowds of fans may put words that have nothing to do with the company or what’s being filmed. When “Insurgent” was filming in Atlanta, its signs read “mineral,” and Walljasper says with its follow up, “Allegiant,” the code will be similarly random, “amnesia.” When this happens, Walljasper says the best thing to do is wait and keep an eye out for the signs. Over time, you may pick up enough clues to figure out which production the signs belong to. (Or just ask Twitter.)

Lastly, if you’re desperate to know what’s filming around town, you could just follow the arrow on the signs. (Most of the time, that is. Walljasper has heard of one case where a production company had arrows pointing in the opposite direction of filming). Though, don’t expect film and TV crews to be excited to see you. Walljasper wants to remind everyone that these are professionals working long hours. Anyone interested in watching a TV show or movie being filmed should do so with respect for the crews.