There like this on the 1.8T Golf's too, and I'm pretty sure many other petrol VW's.Normally the easy way to check if it is a Diesel when not running (or overtaking and can't hear it) is to have a quick look at the exhaust pipe - they are hidden and curved down on VW diesels.... easy to check when looking at the badge.
as seraph has said, this question comes up many times and there is no answer except its completely random, whatever the dealer decided to stick on, I've got a turbo with silver gti, other people have 2.0 with gtiafaic, and as said above and many times over the years, the badges mean little
1) the dealers put them on randomly
2) owners mix and match them irrespective of the car.
'I' has tradionally always stood for injection, hence the acronym, gti : 'grand touring injectiong'