I'm no expert on model history but the trophy reads "Sponsored by Greater Detroit Plymouth Dealers." It probably is from the Plymouth contest series, sponsored by Plymouth Motors, that was a big deal around 1950, in the East and Midwest of the USA. There are others on this site who surely will have detailed information and hopefully will chime in. How it made it to Sydney may be lost in the mists of time. Detroit is in the State of Michigan of course, but the trophy probably has nothing to do with the State of Michigan per se.