Where I work we used to wrap up our work day at 4:45 pm. Yeah, I know that's a ridiculous time but I didn't make the rules; I just followed them. It coincided with our 37.5 hour work week, which apparently is/was a community college thing.
Anyway, every day at about 4:44 someone would call me at my desk, wait for me to answer, and then hang up. We had these old clunky multi-line phones without any caller ID display so I couldn't tell if the call was internal or external or what number it came from.
I was pretty darn sure it was an internal call from someone checking to see if I were still at my desk or if I had snuck out early. Once and while I would even answer the phone, "Yes, I'm still here." And of course, they would immediately hang up. I had my suspicions on who it was but could never confirm or deny those. I told anyone who would listen about my mysterious 4:44 pm caller and my suspicions on why they were calling, but the calls never stopped.
Then one day our phone system got upgraded to a shiny new system that included caller ID. The calls immediately stopped. So yeah, it was totally internal.
The Fine Print: Christmas card.... I made 'em with products from places. Yeah, that's all I got because I'm at my desk working right now. Go ahead, call and check.