The theft of a car is hardly something you are likely to overlook — but the theft of number plates is a different matter entirely. 

At a glance, you might not notice they have gone, especially if they have been replaced by another set.

While hundreds of plates are reported stolen each year in South Australia, the Royal Automotive Association said it had noticed a rise over the past 12 months, linking the trend to petrol price rises. 

"We've been looking at some of the stats and … we think there's been about a 15 per cent increase in number-plate thefts," RAA automotive policy senior manager Mark Borlace told ABC Radio Adelaide.

"The reason they're getting knocked off is because [thieves] want their identity hidden.

Petrol has become an increasingly valuable commodity in recent months, with the price soaring amid Russia's invasion of Ukraine.

Prices have continued to climb, and unleaded is currently hovering around $2.25 a litre in Adelaide.

Mr Borlace said that as fuel thieves targeted petrol stations, covering their plates was one way they could not only cover their tracks, but create a false trail.

"The reality is that number plates are stolen for a couple of reasons, and one of them is petrol drive-offs," he said.

"If the stolen plates are put on by a person who's got a large four-wheel-drive [and] they fill up and drive off without paying, that could be a $100 or $200 bill they've left.

"If those number plates are linked to your car, the police are going to look at that number and come back to you."

Driver notices neighbour's plates on his car

ABC Radio Adelaide listener Alex said his front number plate was recently stolen from his car parked out the front of his home.

But because the plate was switched with another stolen one, he didn't initially notice.

"I didn't realise they were stolen until I drove it into the city and put it into one of those car parks where you then have to put your registration in to pay your fees," he said.

"I looked at the number plates and realised there [was] something strange here. That's when I realised I'd had my plates stolen.

Mr Borlace said some drivers had only noticed their plates had been stolen when they received fines for crimes they had not committed.

"You could get a speeding fine in the mail for a vehicle you weren't driving — that may be the first time you know about it," he said.

"If they get stolen, there's inconvenience. You can't drive your car without number plates so you've lost use of your car for at least a week."

Mr Borlace said one ambitious solution was retiring number plates altogether and replacing them with digital devices.

"The number plate is pretty old technology — it's a piece of pressed aluminium stuck on the front and rear of the car," he said.

"There have been some studies done of having electronic recognition of the vehicle, so similar technology that's used to collect tolls.

"You'd actually have a transponder on your car that would have the effect of a digital number plate."

But, in the meantime, Mr Borlace said motorists could take some lower-tech steps to protect their plates from being pilfered, including by getting "tamper-proof screws".

"They're screws with a metal protrusion," he said.

"You screw them in and when they get tight the protrusion snaps off and you're just left with a dome."