The number 666, traditionally associated with the "number of the beast" in Revelations, appears three times within the number 66666. If I believed in bad omens, I suppose I'd be worried about even seeing that number.
But maybe 666 isn't even the correct bad number. Recent research on ancient Biblical documents indicates that the number of the beast might be 616, not 666.
Furthermore, there are several views among Christian theologians as to the real identity of the beast. My church (Lutheran Church Missouri Synod -- LCMS) teaches that the beast was a symbol of the Roman Empire that was persecuting Christians mercilessly at the time that Revelations was written.
For more information about the book of Revelations as the LCMS understands it, see "A Lutheran Response to the Left Behind Series" (pdf, 908KB).
That odometer reading does worry me a little though. My car's a few miles overdue for an oil change, and I need to get that done soon!