Anyone know what the diff is between the two 1.8T emblems? There's one with a red mark on the right side of the "T" in 1.8T, and there's another with no red mark.

So far, I've only seen the ones with the red mark on the A4's

 

Depends on the year. On a B5 I believe the red T signifies sport package. On a B7 however it just depends on the year and doesn't seem to mean much of anything...

Someone correct me if i'm wrong.

 

Not sure about sport or not after 2000. But the red "T" didn't exist until 2001 and my B5 (2000 with sport package) was not red.

 

I believe that the red "T" was a slightly higher horsepower 1.8T that later became the standard output.

Check out Wikipedia, I think it explains it if you look up the history of the Jetta.

 

Good point ! The B5 had two different power outputs. The 2000 1.8t had a 150 hp KO3 whereas the 2001 (with red "T") had the KO3 sport with 170 HP