Shakespeare's birthday is always an important date at the Folger Shakespeare Library, 201 East Capitol St. But this Thursday -- his 417th -- a day-long festival also will mark the reopening of one of the best Shakespeare libraries in the world after two years of having been closed because of construction. For the first time in the Folger's 49-year history the Reading Room will be open to the public (5-7 p.m.) and Folger's "possible" signature of William Shakespeare will be on view. (Only six authenticated signatures exist, all in England.)

Folger curators do not say that "their" signature is genuine, but they are terribly protective of it. New York autograph expert Charles Hamilton says, "I haven't examined it, and they've never asked me, but it's probably a fake. If anyone ever came up with an authentic document signed by Shakespeare it could probably fetch $1.5 million."

That made me want to see whatever it is that the Folger has. So after visiting the Reading Room, where generally only scholars are allowed, I was told I might be allowed to visit the underground vault where the signature is kept and maybe talk with the curator of manuscripts. As for the signature? "Let's see if we can get into the vault first," said a Folger spokesperson. "Few people do."

The vault is a temperature-controlled room with gray metal bookshelves. Laetitia Yeandle, curator and expert in Renaissance paleography (she can interpret medieval handwriting), was ready. As we walked into the room, she repeated: "No one knows for certain, of course, if it really is Shakespeare's handwriting. It is a possibility. That's all we can say." She pointed to the section that contained the signature.

Where?

"There," she said, indicating a pale blue box. "The book is in that special box. The signature is on the title page of that book, but it was written over a decorative border and it is very difficult to see. The best way to see it is to turn the page and use a mirror to make the signature readable where the ink has leached through."

Yes. But may I see it?

"Well, no," she said. "It is extremely fragile. But we will have it on view for a week. You can see it then."

Aw, c'mon. Can I least see the book, then?

"I'm sorry," she said politely. "We can show you photographs of the signature."

Laetitia Yeandle was adamant: She would not remove the book from its protective cover. "It's very rare that anyone sees it," she explained.

Looks to me as if it could be the real thing, the way you're treating it and all. Is that a possibility?

She would not budge: "The signature could be genuine. That is possible . . . We cannot say for certain. We simply do not know."

But Giles E. Dawson, curator of books and manuscripts at the Folger until his retirement in 1968, went further. Dawson, who was there for 36 years, originally identified the signature as possibly that of Shakespeare when a Folger bookbinder first spotted handwriting in the book.

"It looked good to me then, and it still does," he says. "I think that there is a very good chance that it is indeed the signature of William Shakespeare. All the arguments, and I know most of them, are in favor of the signature being genuine."

When the binder pointed it out to Dawson, "we went over to the men's room and help up the leached page to the mirror. The binder said, 'It looks like Slatyer.' I said, 'No. It's 'Wm. Shakespeare.'"

The book, "Ancient Laws," was printed in England in 1968 and came from The Garrick Club in London. "The Folger picked it up in England at an auction in 1936. It came with several others at the tail end of the auction and was purchased for a pound," says Dawson.

A note on the same page says: "Mr. Wm. Shakespeare lived at No. 1 Little Crown St., Westminister. N.B. Dorset Steps." But, Dawson adds, "no one knows, of course, if Shakespeare ever lived at such an address or who wrote the note."

Autograph expert Hamilton disagrees: "Possibly the reason why the book has not been singled out all this time is that the signature has always been considered a fake. I'll bet it is, even though I haven't seen it."

Check it our for yourself on Thursday.