A friend who collects pens gave me a copy of an ad for the Conklin Crescent
self-filling fountain pen that has a 1903 endorsement   by S.L. Clemens.
(The
add features the pen, an image of the white-maned Clemens, and a facsimile
signature.)
She tells me that Clemens may have endorsed other pens and she is looking
for
other ads.

The copy reads:

New York, Oct. 1, 1903

Dear Sirs:
I prefer it to ten other fountain pens, because it carries its filler in its
own stomach, and I cannot mislay it even by art or intention. Also, I prefer
it because it is a profanity saver; it cannot roll off the desk.
Very truly yours,
S. L. Clemens

(The pen had a filling mechanism that projected from the barrel and would
keep the pen from rolling.)

Did Twain/Clemens typically write such ad copy himself? Was it more likely
that an advertising agent concocted a likely quotation and applied it over
the
Clemens signature? Has anyone done any work in this area of Twain's
endorsements?

Dennis Kelly
San Francisco