Universal doesn't need to theme its roller coasters and as people on the forums will quickly point out, most guests don't care. But what they chose to do with this building is pursue the uncanny valley of themed architecture and split the difference. For theme park fans that love theming and post-Harry Potter, post-Epic Universe, expect that, it's not enough. For guests for whom theming never crosses their minds, it could just look dirty.
There are things about the building look brand new like they could be in a modern mall, even City Walk, like the retail store with it's modern signs and modern door:
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There are things that look almost kitschy or cartoonishly themed from the 1990s (I'm getting DCA vibes here), like the entrance sign:
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There are aspects that are unclear if they are themed or just a mistake, like the "damaged" concrete where the railings are mounted. I honestly don't know if this is intentional or not, as this kind of deep-cut Joe Rohde-style weathering and structural history is not typical elsewhere in this project:
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Overall, the building just looks like a slightly dirty brick building that could have been built any time in the past 100 or so years, especially early in the 20th century or in the post Camden Yards retro-architecture revival of the late '80s-'90s. That is, it looks like this is just a building Universal Studios built in 1993 and it's due a power washing.
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Because it it's themed as "dirty" rather than "really dirty" then it would be useful to make that clear with something more obvious like these actual old buildings in Los Angeles like a faded painted sign on the brick walls or water tower:
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