HSV stands for Holden Special Vehicles. They are an aftermarket company which is joinly owned by Tom Walkinshaw Racing Group (TWR) (75%) and General Motors - Holden Australia (25%). They have a close affinity with both these organisations.
HSV take base model Commodore cars and derivatives and produce 'special' versions. Mostly this consists of performance modifications, body kit extensions and re-apholstering. But these things are only the physical things. HSV have with their marketing, created their own special image which goes beyond the plain-jane cars they start with to excite a whole bunch of people into buying their cars. They have produced several 'one-off' vehciles (eg. a special Gycol-free car for a family who had a special medical condition) and several 'Collector's Edition' cars.
Customer loyalty to the company is huge, with turnover of vehicles low, and resale prices high.
The logo is an amalgamation of the Holden logo (the lion) and a Racing Driver, which highlights the profile HSV has with the Australian Touring Car Championship through the Holden Racing Team (HRT).