I already found something called "Paris Metro Font" on dafont.com, but it's a lot blockier and curlier.

Search for "art nouveau" (like on MyFonts).

hhp

The signs were hand designed by Hector Guimard in the early 20th century, and are not all identical (depending on when they were redone or replaced). Many fonts have been created based on them, but you're unlikely to find a precise match. Linotype lists it as an Art Deco face, some others describe it as an Art Nouveau style

There are a number of different fonts and equivalents, mostly named "Metropolitain". Many are copies or clones of each other.
Dieter Steffmann's was based on Rakowski's Paris Metro
Elsner and Flake has one
Michael Bujardet

Metropolitain VerDover (Dan Solo)
Metropolitaines (URW)
Metropolitaine (Linotype)
French Bean (SWFTE)

- Herb