(One of the perks of not working in a traditional office.)
I used to work at an office where birthday greeting cards were passed around at least once a week. When the card reached me, I'd quickly scribble down a message and pass it on ASAP. One day, a co-worker (and friend) told me that I might want to pay more attention to when signing cards, since the one that had most recently made the rounds was not a birthday card but rather a sympathy card for a co-worker whose parent had recently died. In it, I had written, "Hope it's a great one!"