We love a good architecture mystery here at Curbed, and there’s been quite a doozy–that also involves the New York City subway!—making the rounds on Twitter this week.

It all started with a tweet.

Filmmaker Amy Nicholson shared a photo of this entrance to the 68th Street subway station, near Hunter College, and it left many architecture and subway buffs—this writer included—totally puzzled. Pentagram’s Michael Bierut tweeted about it; so did Curbed’s architecture critic, Alexandra Lange. How had we not noticed that sign before? And further, who was responsible for it?

It’s located in a subway entrance on the southeast corner of 68th Street and Lexington Avenue, and was added as part of architect Ulrich Franzen’s ambitious Hunter College expansion, completed in 1984. Franzen’s two-building design is most famous for adding the two skybridges that connect Hunter’s east and west buildings, but he also commissioned artists (like Tony Smith, who contributed the hulking sculpture Tau) to pitch in with various aspects of the design.

The plaza, designed by Ulrich Franzen, of Hunter College’s Upper East Side campus.

The revitalization of the subway entrance (which, by that point, was apparently among the most deteriorated in the transit system) was part of Franzen’s larger project. It was intended to be an extension of the Hunter campus, with some of the design elements used in the buildings—such as the pink granite of the public plaza—extending underground as well.

That was the biggest clue to who created that signage; Peter Blake’s The Architecture of Ulrich Franzen, notes that the architect called on artist and Supergraphics pioneer Barbara Stauffacher Solomon to “design all of the graphics for the new buildings.” Was she also responsible for the subway signage?

“It was me, I did it,” Solomon told Curbed by phone from her home in San Francisco. “I did all kinds of signage for Hunter.” Solomon had gotten to know Franzen (who she affectionately refers to as “Ricky”) through a friend who had worked for him; the partnership on the Hunter buildings sprung from there, even though she was back in her native California after a period of living in New York City.

Another example of Solomon’s typeface in use at Hunter College, from a 1994 issue of the Wisterion.

There are other markers—both in the subway and in the Hunter buildings themselves—in Solomon’s same breezy typeface, which was a shift from the modernist style that Franzen was known for (as well as for Solomon, who studied at the Art Institute Basel in Switzerland).

“The subway sign makes sense for her to have done, since it is a little bit commercial, a little bit oversized, but definitely personal,” Lange said in an email, noting that Solomon’s work “highlights and supersedes the architecture.” That’s certainly the case at Hunter; though signage in the standard Helvetica would have been appropriate, it wouldn’t have been as surprising or visually interesting.

And besides, “[Franzen] didn’t want Helvetica,” Solomon remembers. “He wanted something more jazzy,” hence the signs we see now. (With a laugh, she says that the design team used to refer to it as “sleazy Helvetica.”)

So the next time you’re passing through the 68th Street station, take a moment to disembark and admire Solomon’s handiwork, which can still be found on both the mezzanine level of the station, as well as in the entrance on the southeast corner. Solomon, meanwhile, is now the subject of a book by Hall of Femmes, which chronicles the work of pioneering female designers; it’s well worth finding out more about her expansive, impressive career.