The wards (and certain residents) prevent anything untoward appearing inside Hellsing's walls - if Mabel ever sees a shadow blink, however, well. That's just Alucard.

"'Monsters' could be the catch-all term," she says. "Vampires, werewolves, demons, ancient creatures, magic-engineered beings, unseelie fairies, and so on. If it's not of a mortal nature and it's too bothersome or too expert for the Militia to see to, then we handle it. We have an all-terminate policy for offenders who refuse to back down on the first request - while some beings may be acting out of fear or the notion that they have no other options, we do not sit about wringing our hands and allowing more civilian casualties to pile up."