So did the Plymouth Valiant name come from a french cartoon character?

My bet is the name came out of a group exercise to choose a name from a dozen or more in a bucket. FWIW, the Prince Valiant comic strip was very popular about that time, so I'd be inclined to go that route. However....Exner tapped European styling cues for many of his designs, so perhaps he did borrow from the French cartoon.

More puzzling is where they came up with Signet. Today it's common to pick any letter jumble that rhymes, or sounds catchy, as names for cars and kids. In the late 50s, it was unheard of.