The creators of Batman: The Animated Series Intentionally invoked this trope to make when the series takes place ambiguous, largely as a nod to Batman's invention in The '30s.
- The buildings are all (or mostly) Art Deco style. Indeed, the art style has been described as Dark Deco.
- Men's fashion seems to be 1930s-40s-era with fedoras being quite popular, though men's fashion tends to change slowly, while women's fashion is more 1940-50s-era.
- Multiple rigid airships are seen throughout the series, though the practice of building large rigid airships (zeppelins) went out of favor after the crash of the Hindenburg. Airplanes, Batman's futuristic fighter jet excepted, are generally powered by piston engines. One episode prominently features an autogyro.
- Computers, VCR and video games are common, not to mention things like digital phones, satellites and virtual reality, yet television broadcasts are in black and white. From its graphics, the Fictional Video Game The Riddle of the Minotaur looks like it was made in late 70s-early 80s.
- Gene splicing is known, and this, rather than surgery, provides the explanation for the origins of the Doctor Moreau expy's animal-men... But his laboratory (and pretty much any laboratory seen) is much more reminiscent of classic-movie Doctor Frankenstein's dungeons than a modern research facility.
- Nobody objects to women having careers or Lucius Fox, a black man, being in a prominent position at Wayne Enterprises.
- Uniforms are 1960s-era and SWAT teams exist, but weapons are 1920s-70s, with M1921 or M1928 Thompsons and 100 round drum magazines being very common while police — or at least patrol officers — carry revolvers and shotguns for the most part. The first SWAT team was formed in Philadelphia in 1964, while LAPD formed its famous SWAT team in response to the Watts Riots in 1965 (there's also the Reserve Unit of the Shanghai Municipal Police, formed in 1925 and considered the Ur-Example of SWAT teams). In the occasional flashbacks set at most a decade earlier, police officers wear 1920s-era uniforms.
- Out of police forces, some mooks can be seen equipped with MP40s (a World War II-era SMG), but M16s assault rifles (designed in 1959, and more modern variants were still used at the time the show was produced) can be seen too.
- Cars are 1930s-40s, Liebherr-type cranes exist, helicopters are from the 1980s.
- Various contradictions in in-universe dating:
- Charlie Collins' driver's license
◊ was issued September 25, 1991, expires March 17, 1995 and lists his date of birth as March 17, 1946. - A photo from Thomas Wayne's graduation, which Bruce says happened 40 years prior, is dated 1908.
- Jonah Hex's story is said to happen in 1883 and implied by dialogue to had happened only 100 years before.
- The magazine at the end of Beware the Gray Ghost explicitly has 1992 on the cover.
- Charlie Collins' driver's license
- The Gotham State University football team wears leather helmets and long-sleeved football sweaters, but plays in a domed stadium.
- In the Direct to Video, Subzero, the music Dick and Barbara listen to is almost exclusively 40's-ish jazz with some doo-wop thrown in.
- The tech, fashions and architecture seem to take quite a jump forward by The New Batman Adventures, despite it taking place only a few years after the original run. By the time you get to the flashbacks in Return of the Joker, integrating DNA into microchips is possible.
- In one episode you can see a black and white flat screen television with remote control.
- "Christmas With The Joker" features the tradition of It's a Wonderful Life being played on multiple TV channels during Christmas, which began in 1974 when it fell into the public domain after the copyright was not renewed and it and continued until 1993 when it was deemed a derivative of The Greatest Gift (the story it was based on) and this covered by that story's copyright.
- Overlapping with Company Cross References, characters can be seen reading Tiny Toon Adventures comics in a few episodes. Tiny Toon Adventures ran from 1990 to 1992, ending just after Batman: The Animated Series began.
