It’s been my headcanon that crosses and other symbols only hurt vampires when actively wielded and invoked by a believer in good standing like in D&D, or on explicitly consecrated ground. Always loved that bit in Salem’s Lot where the priest threatens the vampire with a cross to make him release a victim, and promises to let him go if he does, then breaks the promise and tries to burn him with holy power only for the cross to fail because oathbreaking is a disqualifying offense.