GUEST: I was in an estate sale in San Francisco in February.

And the man of the house was French.

And he was in his 80s, and he had a whole wall of them.

Plus a whole bunch more unframed and I fell in love with them, called my husband and said, "Honey!

(laughs) I found something I really love!"

And he says, "Well, go ahead, and buy it, it could be your Valentine present."

I said, "Can I buy one for Valentine's, Mother's Day, Easter, birthday, anniversary..." So, I bought a few.

(laughs) APPRAISER: How-how many did you buy?

GUEST: I bought four framed and eight unframed.

APPRAISER: And-and why did you choose to bring this one in today?

GUEST: I couldn't find anything about it.

I finally found Dunkerque on the map of France, but it was one of my favorites, and so I wanted to learn more about it.

APPRAISER: And how much did you pay for it?

GUEST: Framed, $500.

APPRAISER: You paid $500, so it's an expensive Valentine's Day gift to yourself.

GUEST: Yeah... no, it was from my husband.

(laughing) APPRAISER: It was an expensive Valentine's Day gift from your husband.

It is a French travel poster advertising travel to Dunkirk in the north of France.

And it's advertising travel on the Chemin de Fer du Nord, which is the French railway of the north.

It was designed by an artist named Roger Broders, and Broders is considered to be one of the best, and he's certainly one of the most popular Art Deco artists working in Paris in the 1920s and 1930s.

Now, this poster isn't dated, but through reference books we know that it was done in about 1930.

And Roger Broders is really famous for the travel posters he did for the different French railways because they all have this sort of very exquisite Art Deco feel to them.

The majority of his work is landscapes.

But the pieces of his that really command the highest prices are the ones that depict people.

And here we have an image of a couple who, to me, really sort of bespeak everything "Great Gatsby."

They're an elegant, Art Deco, refined couple with beautiful clothing.

And they're shown enjoying the harbor of Dunkirk.

Now, Broders was such an exceptional artist, I-I've never been to Dunkirk, but knowing how good he is, I can imagine this is exactly what the skyline of the harbor of Dunkirk would look like and the poster was produced not only by the Chemin de Fer du Nord, but also by Syndicat D'Initiatives, which is basically the chamber of commerce.

GUEST: Oh, okay.

APPRAISER: So, the local chamber of commerce, together with the railway, said, "Buy a ticket, come to our town."

He did about 170 different posters.

This poster is one of his two rarest images.

GUEST: Oh, wow.

APPRAISER: It's so important that when they did a catalogue raisonné of all the posters he designed, this was the picture they chose for the cover of the book.

GUEST: Really?

APPRAISER: I did some research, and I was trying to remember what was the most valuable piece I had ever appraised on the ANTIQUES ROADSHOW.

So I actually went onto the ANTIQUES ROADSHOW website and I checked the appraisals that I have done over the years.

And, in fact, this poster ties for the most valuable single piece I've ever appraised.

GUEST: Oh, my gosh.

APPRAISER: And that value, at auction, I would estimate it between $15,000 and $20,000.

GUEST: (laughing): Oh, my God.

(laughing) I can't believe it.

I'll go home and thank him.

APPRAISER: Honestly, nothing says "I love you" more than a $20,000 GUEST: Oh my APPRAISER: travel poster.

GUEST: oh, my gosh.

Oh, my gosh.

APPRAISER: Happy Valentine's Day.

GUEST: (laughing): I know, really.