This is the only image I’ve located for the store at 28 St Marks Place, where I worked in the late Sixties. It primarily sold buttons and posters. Don’t know who the girls are. Photo found at
https://www.tumblr.com/search/underground%20uplift%20unlimited (January 12, 2018).
I highlighted the sign with the UUU logo on it and would be happy to have more images of the store from this period.