A Cup of Jo's Joanna Goddard posted about this print quite a while ago, and I must have missed it originally. While bouncing around her blog this morning I found it. Visit Sophie Blackall's Etsy shop and check out more of her charming work!
This is part of her Missed Connections series, which details posts from Craigslist that depict people lamenting missed romantic / social connections. Such a sweet idea. It reminds me of the first episode of the show Dharma and Greg, where the future couple spot each other through the glass of the Subway train window.