.......or the clearest view of what the prop guy thought his name was.

I think the clearest shot of the Lt.'s name is in "Dead Weight" when Columbo meets the General for the first time. He shows his badge, and, via the magic of DVD, you can see his name clearly reads 'Frank.'

On a related note.....

I'm just back from the Museum of Television & Radio, where I checked out an episode of 'Checkmate' among other shows.

At one point a character played by Diana Van Der Vlis says to the detective played by James Whitmore (both guest stars):

"I don't even know your first name."

His reply?

"Lieutenant."

Wasn't this basically the same exchange between Columbo and Faye Dunaway's character? I'm fairly certain something similar was said in at least one episode, but for some reason this one seems the most plausible.