At least I think it’s number 6-13… that number is one of many things written on the back, and it’s in the format of many other numbers on Times Square photos and slides.

Based on her shirt and wig, my best guess is this is from a scene that didn’t make it into the film, after Nicky’s been arrested but before she’s sent to the hospital, where she’s being observed from behind a one-way mirror. There’s another image from this scene that was published in the Australian Women’s Weekly, Vol. 48 No. 45, April 15, 1981, that shows the mirror. It comes from a slide named 5-19A, which I have but haven’t gotten around to posting yet. (Send enough donations through the Ko-Fi link below to free up my time and you’ll see it right away!) The scene appeared in the May 1979 draft of the script starting on page 10, featuring an observation window and not a mirror, but that could easily have been a change made before shooting. Robin had also described improvising a scene in front of a one-way mirror as being part of her audition, in an interview in Seventeen magazine, that used this very photograph. 
Among the various things written on the back of this print is “Oct P8-98.” While I don’t have the issue handy to check page 8 (if I locate it in my collection I’ll edit this post), Robin’s interview ran in the October 1980 issue of Seventeen, on page 98. I didn’t realize it when I bought it, but I think this print is the actual object that was used in 1980 by Seventeen magazine in laying out the page.
Today marks 46 years since Times Square opened in general release in the USA. I saw it either that evening, Friday, October 17, 1980, or maybe Saturday the 18th, and then once again the next week, and then it closed and went away, apparently forever… but we’re both still here…