When Damon and Vicki and partying in the Salvatore boarding house, Damon often paces through patches of sunlight yet does not burn or seem hurt despite the fact that he does not have his ring.
In the flashback, Katherine does not put on her daylight bracelet.
In the flashback scene where Katherine asks Damon and Stefan to take her to the Founder's Ball, Damon uses his left hand to remove his hat as he bows down. In the next shot, Damon puts his hat back using his right hand.
In the state of Virginia (where Mystics Falls is said to be) if you are under the age of 21, all IDs are supposed to be vertical. However, when Sheriff Forbes looks in Viki's purse her ID is horizontal.
Near the beginning of the episode Sheriff Forbes finds Vicki Donovan's driver's license and holds it up. You can't see the date of birth but you can see that the license was issued in the year 2000. This would have been impossible for Vicki, who is only supposed to be 17/18 in 2009. She would have been 8 or 9 in 2000.
In all the other times that either Damon or Stephn have been cut, the wound healed almost instantly. However when Damon pierced his own skin to force Vicky to feed, the wound stayed open for the entire time she was drinking from it.