My GN has a red T on the horn button as well. i have read stories of GM either running out of the tri shield or something to that effect. The tri shield is correct and I have been looking for a nice one that is reasonably priced for awhile.
My gn I bought in 88 was one of the last ones off the production line(from what I recall) and it had the buick tri-shield. Both of my gns had the tri-shield
ALL !! GN's came with the trishield emblem in the horn cap but replacment ones went away in the late 90's, so when ordering a new one all you could get was the Turbo-T one. That being the red T medalion.