Theft resistant number plates : Directgov - Motoring
About halfway down there's a link to "The Criteria for Theft Resistant Number Plates"
I'll leave it to you to check out, but just take a look at the list of tools that number plate thieves carry round to do the dirty on your beloved Alfa
Tool List
Club Hammer (1 Kilogram)
Hammer (1Ib)
Pry bar
Chisels
Punches
Centre Punch
Wedges
Screwdrivers
■ Slotted tip
■ Pozidrive
■ Philips
Abrafile
Hacksaw
Padsaw
Craft knife
Tinned Copper wire
Waxed twine
Cheese wire
Battery drill
■ Drill Bits (1mm – 13mm)
■ Hole saw
■ Screwdriver bit
■ Pozidrive bit
■ Philips bit
■ Screw extractor
Pliers
Allen Keys
Sockets and Spanners
Vice grips (moles)
Hot air gun
Palett knife
Double Sided Adhesive Tape
Solvents
■ Petrol
■ White Spirit
■ Metholated Spirit
■ Paint Thinners
■ Bleach
On the plus side - if you ever need to get a number plate off, you now know what to use.
