To my Chicago readers: Is it the L, the ‘L,’ or the “L”?

Yesterday I got back the copyedited manuscript for Lovecraft Country. Most of the corrections are straightforward, but one of my copyeditor’s notes has raised the question of how to properly refer to Chicago’s elevated transit system.

I know that Chicagoans traditionally call it the L, not the El, but what I’m having a harder time deciding is whether “L” needs to have quotation marks around it, and if so, whether they should be double- or single-quotes. My instinct is to omit the quotes, as I think L tracks looks cleaner than ‘L’ tracks or “L” tracks, but then again, as a native New Yorker, my instinct would be to call it the El. A survey of the CTA website, the Encyclopedia of Chicago, and various other sources suggests that L-with-quotes is more common but not universal, while the choice between single- and double-quotes is largely a matter of personal preference.

Any fans from Chicago want to weigh in, or better yet, point me to a definitive monograph on the subject? Note that the novel is set in the mid-1950s, if that matters.