A girl works reception in an office (not same company) down the hall. Same floor but we do not run into each other in the hall. I smile as I pass by, but any approach would be obvious to multiple people in a smaller room. Even entering the room would be set the others off thinking I was visiting for a business reason. Flirting with her straight up I think would likely be uncomfortable for her and everyone else in the room.

I've tried the waiting game hoping for the random run in in the elevator or hallways, but our work schedules don't match so it doesn't happen. I've considered walking in, just confidently saying "Hi", smiling and leaving her a note...