Apologies if it seemed I was disagreeing with you. As a pastiche wouldn't "S3" have made more sense ? I like this story (often quoted online): The first car number plate ‘A1’ was famously issued to the Earl Russell, who made his butler queue up overnight at the London County Council offices to secure it back in 1903 when the Motor Car Act was implemented by parliament.
Peter 2009 3-litre Roadster "Ivor", royal ivory / green