If the uniform number notation "33" inside does indeed correspond with Eddie Murray, then it's significant because Murray could only have worn this jacket in 1996—the same season that he joined the 500 HR Club.
Authenticator Phil Wood's LOA says everything you need to know: "The Orioles wore this particular style of jacket from 1995-99. The '33' inked into the collar would seem to indicate it was originally issued to Eddie Murray, who returned to the Orioles on July 21, 1996, following a trade with Cleveland. He played in 64 games for Baltimore that season, with 10 home runs, including the 500th of his career on 9/6/96. In 1997 he finished up with the Angels and Dodgers and was inducted into the Hall of Fame in 2003. All that can be said about this jacket in terms of authenticity is that it's a real Orioles jacket of the aforementioned era. The inked-in #33 really doesn't guarantee anything. Certainly Eddie Murray would've worn an XL jacket; by the end of his career he was wearing a size 48 or 50 uniform jersey. However, because Starter never saw fit to use any kind of year tagging, and fans could buy this exact jacket 'off the rack' at the team store at Camden Yards, it's impossible to state with any authority—beyond a sworn affidavit from the ballclub or Murray himself—that this was Eddie Murray's Orioles jacket. It's in great shape, still very wearable, and a style that's no longer available."
Wood also offers interesting background info about Starter: "The history of the Starter brand dates to 1971. Founder David Beckerman launched the business in New Haven, CT. In 1976 Starter was granted a non-exclusive license by MLB to produce jackets and accessories. By the 1980s most MLB teams were wearing Starter jackets on-field, though in many cases, jackets from previous years from other manufacturers were re-used, and teams were under no obligation to wear the Starter jackets. The Starter jackets were more prominent throughout MLB in the 1990s, though their MLB license expired in 2000. Nike purchased Starter in 2004, and sold it to Iconix Brands in 2007."