Today, coming out to my van from buying groceries, I realized that there was actually a minor dent in the front bumper. Upon closer examination, I found a large scrape on one end of the bumper where some of the molding was worn away. I have no idea how all of this happened, but it looks to me like possibly the afternoon before I left for Worldcon, someone had a minor collision with my front bumper, inflicting all of the damage above, but that I was too distracted by trip plans to notice anything except the front license plate.
This is annoying, and it's probably not worth trying to have it repaired, but I guess I should be grateful that it wasn't a full-blown collision that would have totaled my van just before we headed off to Anaheim.
Edit, 9/4 9:50: Corrected typo noted in comments.