This is the shirt, im trying to find more info on the creator ("Bill Green"), and this image (below) from the website http://www.bambi-amiga.co.uk/amigahistory/rareitem.html
is the only mention i could find of it
The company on the tag is "Screen Stars Best"
(update: the shirt from the picture is from the first Ami-Expo in San Francisco in 1987, but the one i have is from chicago, they seem to be the exact same shirt however)
http://www.bambi-amiga.co.uk/amigahisto ... miexpo.jpg