Driving the streets of Los Angeles, it is hard not to notice a consistent layer of unusual yellow signage lashed to fences, strapped to streetlights and hung on signposts.

With over 10,000 produced per year, these placards are so common today a visitor could mistake them for city-sanctioned signs, which, in a way, they are: the city ignores them because they serve the film industry, which in turn drives the local economy. The signs are so ubiquitous, they have even starred in their own music video:

The format of these signs is consistent, if a bit confusing at first glance: a word or acronym written forward and backward in black, above and below a directional arrow, all on a bright yellow backdrop. The lettering is frequently stretched or compressed to fill the one-size-fits-all confines of the prefabricated placards.

The design makes sense upon reflection: each sign is modular and can be flipped upside-down in order to point left or right. The now-standard look of this 18-by-24-inch yellow sign evolved to help industry workers get to filming locations, with titles simultaneously intended to mislead anyone not in the know. They tend to feature fictitious names and acronyms that sound absolutely dull – real titles would lead fans and press to secret locations.

“Corporate Headquarters” was used for the “Star Trek” reboot until fans figured it out; new signs were printed with “Walter Lace” as a replacement code.

In some cases, the names contain insider hints only those working on a show or movie would recognize. Some folks familiar with the comic book character might realize “Freezer Burn” was a reference to “Captain America;” the fictional WWII hero spent decades on ice before reemerging in the present.

The fake names have to be distinctive, but funny ones are frowned upon: if they are too strange or entertaining, the signs will be stolen.

In the modern world of Google Maps and GPS systems, these might seem redundant, yet they are more popular then ever. “If you’re working on a film, the day before … you’re going to be given a call sheet,” explains Jim Morris, General Manager of JCL Traffic Services, the main producer of these yellow signs. “And attached to that call sheet with what time to show up is going to be a map.” This packet will be sent out to everyone the night before, from special effects and props people to lighting technicians and talent. There is not always a simple address available to plug into a GPS system and some of the shooting locations sprawl or change over the day, so the yellow signs are essential to get people where they need to go in an efficient and reliable manner.

The sheer obviousness of these signs seems like it could work against the aim of staying under the radar. However, as Morris points out, the sheer volume of filming that happens in Los Angeles renders them effective at blocking die-hard fan of specific television shows or films. Few people are interested in following coded trails when there are so many shoots going on just about anywhere. Fanatics, Morris also notes, tend to find a way to target locations, one way or another; the lack of signs will not stop them.

Deviating from the standard yellow sign design tends to create problems. Morris relayed a case in which a client asked for fancy navy signs with white letters: “We made about 300 of those one time and after about three days they were back and said: ‘Give us new ones! Everyone’s driving right by these things … you can’t see them! Everyone’s looking for the yellow signs.'”

The more you think about their function, the more logic you can see behind their standardization. Just like official city signs, these need to be consistently recognizable and visible in order to serve their sizable target audience of film directors, stars, crews and extras … a rotating cast of drivers forever crisscrossing the City of Angels.