Published: 28th August 2008 | Author: Sky News Website
The blue traffic information notice shows a satellite above a lorry with a red line through it.
But the message may not be clear enough for some because the words sat-nav do not appear.
Traffic engineer Mark Simpson came up with the design after more than a dozen lorries got stuck on a small lane between the M4 motorway and Cardiff airport over just a few months.
Authorities are now hoping to see the end of major travel disruption caused by stranded vehicles in the area.
Four of the signs have gone up around St Hilary in the Vale of Glamorgan for a year-long trial after the Welsh Assembly agreed to the move.
The lane already has signs saying "Unsuitable for heavy goods vehicles," but many foreign drivers do not understand them and follow their sat-navs instead.
MrSimpson now hopes his sign will be rolled out across the country.
He said: "Sat-navs can be a wonderful tool but it has its dangers.
"We've had a series of problems with drivers getting into trouble by trusting their sat-navs and we needed to do something about it."
One St Hilary resident told the Daily Express: "This was a nice quiet village where the only traffic we needed to worry about was tractors. But since lorries were equipped with sat-navs it has become a nightmare."
Other villages affected by such problems include Millers Dale in the Peak District, Stroat in the Forest of Dean and Mereworth in Kent.
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