An electronic road sign in the small South Dakota town of Dell Rapids has been displaying a viral anti-Joe Biden phrase in recent days.

       Let's Go Brandon has become something of an esoteric rallying cry for critics of the US president, as well as for conservatives more broadly.

       On this particular sign, the message ended with the less than subtle ‘FJB’ abbreviation– or ‘F*** Joe Biden’ for the uninitiated.

       Generally used to flash warning messages to drivers in Dell Rapids who are approaching a construction site, it's not yet known who is responsible for the sign, as perThe Daily Beast.

       The phrase has gained a huge amount of traction online, although views differ on whether it is simply a meme, or something more akin to a right-wing dog whistle.

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       The phenomenon dates back to a television interview with NASCAR driver Brandon Brown in October. After a section of the boisterous crowd started to unmistakably chant the words “f*** Joe Biden”, the interviewer instead suggested that they were shouting “Let's Go Brandon”.

       (Getty Images)

       The phrase has since been used as a code by many people, in order to subtly convey their true feelings about the 46th President. While the road sign may actually be the work of pranksters, it does speak once again to the enduring popularity of Let's Go Brandon.

       The Dakota Department of Transportation has since manually switched it off, adding that they have no further details on who programmed the sign in such a way.

       Dell Rapids Mayor Tim Earley was similarly perplexed, while State Rep. Tom Pischke found the stunt altogether more amusing. As the Daily Beast reports, The Republican posted a picture of the display accompanied by laughing emojis.

       The Dell Rapids example is just the latest in a series of Let's Go Brandon related incidents. Over the Christmas period, ex-police officer Jared Schmeck ended a phone conversation with the President and the first lady by saying: “Merry Christmas and Let’s Go Brandon!”

       Mr Schmeck has faced a backlash online for his brazen stunt, after the Oregon-native was pictured wearing a MAGA hat, and making an appearance on Steve Bannon’s podcast.