I have field-verified this: there is indeed a no-right-turn restriction from 12th Street into the alley. And a no-left. In point of fact: it's now a one-way going eastbound, you can't enter the alley from 12th at all. As such I've deleted the turn restriction added here and made a final section of the east end of the alley an eastbound one-way. See https://www.openstreetmap.org/changeset/164874198 :)