This is true according to Snopes:
http://www.snopescom/autos/theft/gastheft.asp

A woman said her son found his license plate missing so he called the
police to file a report. They told him people were stealing the plates
to get free gas. Given the rise in gas prices, people have taken to
stealing license plates, putting them on their car, then getting gas and
running. The gas station will have "your" license plate # and you could
be in trouble for "pump and run." Check your car periodically to be sure
you still have a plate. If you should find it missing, file a report
immediately!!! Keep an eye on your license plate! Make sure you always
know it's there! When the license plate is reported as the "drive off
vehicle", it's YOU they contact! Be aware!!!! Be aware of your license
plates, most of us never look to see if they're there.

I DID NOT NO THAT ,NOT GOOD AT ALL:

Is this trend actually happening?

I mean...doesn't seem like much sense. If they have the patience to
carefully take off your lisence plate (some have alarms) why wouldn't
they just stick to the old fashioned way of stealing gas....siphoning
it?

Also, cops will EASILY tell the plate is stolen. One a plate is run, the
color/year/make/& model appears on the screen. No need for widespread
panic. The victims of the liscence plate theft will not be held
accountable. The plates are registered with the make/model and color of
your car, even your tabs are registered for your car! If someone tried
stealing your tabs they would not work on another vehicle. Even if you
bought tabs and lost them....the cops can still run your plate and know
that you have paid, good to know eh?

In some areas, the gas siphoning is so out of hand that basically
everyone who leaves their car on the street uses the gas-caps with the
lock in them.

I got pulled over last week. Apparently the state had not updated the
computer system so the tags on my car were reading some crapola that my
vehicle was owned by a huge "rent a wreck" corporation..LOL and it had
expired in 1997!!!!!!
Imagine my shock hearing that news!! The lights going off from that cops
crusier reminded me of christmas for sure!!!!