Probably custom. Discussed here several timers before, including
http://www.dafont.com/forum/read/221030/acne-font
The Acne branding is discussed at
https://veroniquemklomp.wordpress.com/2013/09/13/assignment-two-describe-a-brand-acne-studios/
It inludes an analysis of the tiny oval emblem for Acne Studios Stockholm, but no suggestion of a font as source of Acne.
Examination of a high resolution image of Acne:

excludes every candidate I checked, including Pistilli Roman, digitized by Jason Walcott as Eloquent
http://myfonts.us/td-a09PFCFuso orario: CEST. Ora sono le 16:24