How do people visually distinguish Vulcans from Romulans in the Star Trek universe?

Question

After the Vulcans and Romulans split by just looking at one how can you tell the difference? For example on one of the episodes a guy looks at Spock and says he is a Vulcan but how does he know he's not a Romulan?

Answer 1

Context.

Prior to "Balance of Terror", most of the species in the Federation were only aware of one pointy eared, green blooded species. Therefore, any Romulan they met would instantly be a Vulcan in their eyes.

After "Balance of Terror", the majority of Romulans encountered were part of the Romulan Military (on board Romulan ships, wearing Romulan uniforms etc).

Similarly, Vulcans were generally encountered where one would expect to find a Vulcan (Federation or Vulcan starships, bases etc.)

Beyond that, there would be behavioral cues. For example, regarding Amabssador T'Pel:

The script for "Data's Day" ... says, "She is Vulcan, middle-aged, and has the cool, regal bearing common to her species."

Cool and regal are not Romulan traits by any stretch.

On some occasions, such as with Ambassador T'Pel/Sub Commander Selok, Vulcans and Romulans were able to pose as a member of the other species without altering their physical appearance.

• Talok in the 22nd century
• Selok in the 24th century
• T'Paal in the 24th century

The only thing that these characters changed was their behavior, hairstyle and clothing so they would seem more Vulcan or Romulan as the situation required. Unlike Kirk, Picard, Data and Troi-no cosmetic surgery was necessary.

Let's not forget about Simon Tarses who was part Romulan but passed for Vulcan and was never questioned about it until the events of "The Drumhead".

Answer 2

In TOS "The Paradise Syndrome" Spock studies the ancient writing of the Preservers and learns to read it:

SPOCK: You prescribed rest, Doctor. The symbols on the obelisk are not words. They are musical notes.
MCCOY: Musical notes? You mean it's nothing but a song?
SPOCK: In a way, yes. Other cultures, among them certain Vulcan offshoots, use musical notes as words. The tones correspond roughly to an alphabet.

So Spock knows of at least two Vulcan offshoot cultures that use musical notes as words, and at least one that doesn't. These three or more Vulcan offshoot cultures may be primitive ones protected by the Prime Directive and studied in secret or full fledged members of interstellar society that Humans and Vulcans sometimes met. Presumably these Vulcan offshoot people dress and behave differently than Vulcans and so can be told apart.

Furthermore, "Journey to Babel" indicates the natives of Rigel V have a similar physiology to Vulcans and possibly a similar appearance, and possibly are members of the same species.

SPOCK: Doctor.
MCCOY: I see it, Spock, but that was a Rigelian.
SPOCK: Rigelian physiology is very similar to Vulcan.
MCCOY: Similar is not good enough. It's still experimental.

Thus the statement in Geewhiz's answer that:

Prior to "Balance of Terror", most of the species in the Federation were only aware of one pointy eared, green blooded species. Therefore, any Romulan they met would instantly be a Vulcan in their eyes.

Should be only partially accurate in the interstellar civilization of TOS.

Answer 3

While not canon, the book "My Enemy My Ally" by Diane Duane has the following quote from McCoy, which gives a physiological reason.

The quote is discussing a plot to invade a Romulan station with the aid of Romulans (matter of honor), and having the Rihannsu act as Vulcans with each boarding group:

"They won't think that for long, Spock," McCoy said. "Remember, Rihannsu and Vulcan culture have been diversing for thousands of years...and most of the subconscious cues buried in their respective kinesics, their 'body language,' will also now be very different. A Rihannsu would know you weren't one, if he looked long enough, not from any physical divergence- but just from a wrong 'feel.'"

So basically, while a Vulcan may outwardly look like a Romulan, there are ways of walking, acting, talking that are endemic to any culture, and if a person does not fit that, they give off a wrong vibe to people of the culture.

Answer 4

During TOS, Romulans and Vulcans appeared physically identical, and as noted in other answers, differentiation could only be done based on context, attire, or behavior.

TNG introduced a physical difference. As in TOS, Vulcans appear human except for eyebrows, ears, and skin tone; in addition to the Vulcan traits, TNG gave Romulans subtle ridges on the forehead above/between the eyebrows, giving them a slightly more menacing look and an obvious means to differentiate them. It's a more subtle case of the same thing that happened with Klingons between TOS and TNG.

Answer 5

Hate to despoil the trek mythos, but in the The Next Generation sequel series before Discovery and Picard, the main visual difference was that the Romulan brow was more prominent. Watch the visual differences between enterprises T'pol and TNG's Romulan captain Picard plays chess with so often, Tomulok. Vulcans only look different to humans by the ears whilst the Romulan brow ridge would give them away in a flat second. And no I am by no means confusing them with Klingons; watch the videos where they talk about the makeup actors have had to have placed on them to play Romulans.