We have had this discussion before...

...yes, there obviously is some way for vampires to pass as motral. Count Verandis Ravenwatch does it when we first meet him in the game after all.

BUT - there obviously is some drawback to it as well, because he stops doing it, and pretty much all the other vampires your character might encounter don't bother...

There have been some ideas on that mentioned in the past...

A toggle-able skill that works, but takes up a skill slot while in effect.
A special item, that works, but takes up a jewlery slot while in effect.
A special disguise that can only be worn at vampirism level 1 and unequips as soon as your vampire gets hungry (thirsty?).

Personally I would go with the skill, making it lower a vampires appearance by one stage, thus making them look "mortal" at vampirism-1... and then add NPC reactions to vampires not "keeping up the masquerade", at a chance depending on their percieved (meaning having that mentioned skill toggled will use the chance of the appereance, not the actual vampirism stage, so if you are at stage 1, you would look mortal and thgus have zero chance of discovery) appereance... say, 20% at level 1, 40% at level 2, 80% at level 3 and automatic at level 4 - guards would attack the "bloodsucking fiend" at sight, vendors would refuse to deal and scream for the guard instead, and so on.

Of course, I also would want to see a special "vampire only" meeting place, possibly the lair from the initiation quest refurbished with some vendors (selling vampire themed gear, perhaps even bottled blood? ), maybe even crafting stations for a vampire themed outfit range...

And while we're at it, I really would love to see more vampire clichees added.

Now, we don't have mirrors in the game, but... reduce their swimming speed and give them a good reason to avoid running water, perhaps?

And deny them food buffs due to not eating clichee, but add more drinks that have vampire-specific uses?

And especially give them a nice "sneak up and bite neck" cinematic (like Blade of Woe) instead of the "bloodriver suck" we have not. And let that feeding *** -damage- the mobs you feed on, I mean, comparted to blade of woe which insta-kills, draining them to half health through your feeding would be more then applicable, right? Heck, for that matter, let vampire assassins combine their feeding and their killing into a "bite of woe" that sucks their victims dry in one go...

And while we're at it, give them more feeding options. Bottled alchemically preserved blood. Willing NPC "blood donors" in vampire refugee who will let them nibble for a bit of gold. A "charm" skill that will allow them to entrance some civilian ("white glow", those you can pickpocked or murder) NPC to allow a feeding without them screaming for the guard (would still count as crime if someone else saw you, but... catch them without witnesses, and drink your fill without bounty), even feeding from willing player characters, perhaps...