Why should Bethesda be lazy? It is clear that Vampires are recognized by people! "Dont like those eyes you got. They've got a bad hunger to them" "You'r skin's as pale as the snow. Are you scared of sunlight or something?" People obviously notice you being a vampire! Also the loading screen often says, that as a vampire people will comment on your appearance, but they will never shun you like they do the werewolf. Everyone knows about you being a vampire, but as long as you dont harm them by feeding or attacking them they just don't care! They differ between hostile vampires and those who seem to feed only on bandits, as its not their concern ;)