We all usually agonize over descriptions and spend a good deal of our IC time trying to either convince or unconvince others of the character's natures..be it mortal, vamp, cam, or sabbat. One thing people tend to overlook is how humanity affects the appearance of a vampire. So, here's a couple of tips, taken from the VtM Revised (page 134)

Humnaity 7 -- ..Most human beings have Humanity scores of 7 or so, so vampires at this level of Humanity can usually manage to pass for mortals.

Humanity 6-5 ..some minor physical eeriness or malformation may show up at this stage

Humanity 4 - ...Physical changes become quite evident at this stage, while not hideous in the sense of the Nosferatu or certain Gangrel, the vampire acquires a pallid, corpselike and noticeable unwholesome aspect.

Humanity 3-2 ... Vampires at this stage may be physically 'mistaken' for human, but don't bet on it

Those vampires following a path are considered to have a humanity of 3 when interacting with mortals (page 286)...hence there is something fairly "alien" about their appearance.