[b]These suggestions are only apllicable to the Undead sort of vampire. So if no one is cool with these suggestions we can omit and modify them to fit a different breed of vamp that satisfies everyone.[/b]

With a healthy diet of blood, they might not even need make up, since our lively glow stems mostly from the blood in our veins. They feed on blood for their survival but its also a great way to appear more human, thus successfully luring in more prey.

There can be several other instances in which vampires can give themselves away to the keen eye of the living(Those members of The Order could be trained to search for these signs once the information makes itself present [b]in game[/b]):

Underfed Vampires would show more symptoms of the undead: pale, glossy eyes, maybe not as strong as their well fed counter parts, lethargy(sluggish even by human standards), stiffness. Etc. etc. 

Another way to identify vampiers could be scent. Vampires are Undead, lacking in blood, a poor diet results in body odor reminiscent of decay. Since bloat is what occurs first in decaying humans, they'd stink from the inside out. So putrid gaseous breath could be the first major indication of Decay. But this is usually in the case of the extremely emaciated.

A vampire who has not honed in their skill of hunting and luring in prey (Charisma and/or stealth) could wind up exhibiting these symptoms. They'd behave a certain way as well, since they're more likely to be hungry. The behavior of any starved individual can vary (i.e. be left up to the player  ;) ) 

Also a class distinction could develop since those in organized covens would be backed with unified support and a steady source of blood. Outcasts, loners, or the generally uneducated would have a harder time of it and give themselves up to The Order easier. (Or be culled by those higher ups that want to keep their species under wraps and avoid a lowly starving chump to give them away).

As extensive as this is, I like [@Xilaw]'s idea to keep most of this info obscure to the humans in this setting. With that being said, [b]only[/b] vampires would have access to certain clusters of info and only long standing established Covens would have the most in bulk. If there are any humans who would know this info regarding vampires, it'd have to be those who have been in close quarters with them (Donors?).

If anyone has other suggestions, be my guest.