After the Treaty of Algeron, the Romulans had stayed on their side of the Neutral Zone for a 100 years. Nor were there contacts by subspace radio since the Romulan War.
SPOCK: As you recall from your histories, this conflict was fought, by our standards today, with primitive atomic weapons and in primitive space vessels which allowed no quarter, no captives. Nor was there even ship-to-ship, visual communication*; therefore, **no Human, Romulan, or ally has ever seen the other.
When a cloaked ship attacks Federation outposts along the Neutral Zone, Captain Kirk says nobody knows what the Romulans and their ships look like.
KIRK: After a whole century, what will a Romulan ship look like, Mister Stiles? I doubt they'll radio and identify themselves.
STILES: You'll know, sir. They're painted like a giant bird-of-prey.
Lt. Stiles turned out to be correct. They do have a giant bird of prey painted on them.
How did he know?
Did the Federation actually see enemy spaceships from the Romulan war a century earlier? And that every ship they saw had a bird of prey emblem on it?
I have not seen Star Trek: Discovery or Star Trek: Enterprise, so if you have answers from those TV series, please provide them.