Years ago, in almost a previous life, I worked at a call centre. It wasn't a large one but it required somebody to be there 5/24. When I started, I was given the sort of shitty shift (of course) and that shift usually started on Sunday afternoons. The office was usually empty and, once in a blue moon, some sales people would show up. But, because we were put in the corner of the building, we won't notice each other. I knew people was there because of the automatic lights - after 7:00 p.m., lights will go off if it didn't detect motion for ~10 minutes. Did I jerk myself once in a while? Hell, yeah - specially when nobody called and there were no emails to reply. However, to, ahem, cover myself, I would usually go to the washroom, not in my cube. (It won't have done it in my cube either, as I had the windows cube and there was an apartment building right in front).
I found out I wasn't the only one. After I paid my dues and moved to another shift, every once in a while, I went to the office to catch up on some stuff some times (I lived close enough). There were times it was obvious the person was jerking. Years later, when said person left, I was told he had an external drive full of porn. Didn't ask whether he downloaded at work or he brought it with him. Was it men only? Nope. There was this Korean chick who took over that shift years later (I was team lead by then) and, in one of those days where I was there on the weekend to finish some crap work stuff, I heard some buzzing coming from her cube along with some panting and sighing. Because of the automatic lights when I walked over that area, that sound went away quickly when I went to check. Let's just say she was almost red as a tomato when we had some small talk. The fact she started to look uncomfortable when asked about the buzzing sound told me everything I needed to know - specially when less than five minutes after I went back to my office, she went to the washroom. If it wasn't because I didn't (and still don't) want to be involved with people from work (and, no she didn't report to me but we work close enough to know each other), I would have told her what was in my mind.