from rec.food.cooking:

Here is a question that came up several weeks ago:  How did it become
tradition to flatten peanut butter cookies with a fork and make a
crisscross pattern?

For some reason, peanut butter cookies are almost always made with
this crisscross and no other type of cookie is.  Why?  This is a
question which really came up a few weeks ago and nobody could answer.
 Then I saw this post and thought maybe one of the great posters to
the n.g. would know the answer.

thanks

hahna,

Good question, and after researching this topic for more time than I
expected, I have a powerful craving for peanut butter cookies - and
they MUST have the criss cross marks on top! (Personally, I think this
gives the cookie an extra little "crunch")

Here are the few crumbs I found:

From my own local newspaper, The Arizona Republic, Clay Thompson,
October 12, 2002:

“I recently said that I did not know why peanut butter cookies always
seem to have fork marks on them, and a number of you wrote or called
to opine that only a knucklehead would not know this.
Several people said the fork marks are there to warn off people who do
not like peanut butter cookies. However, the most sensible idea came
from a gentleman who noted that peanut butter cookie dough is by
nature kind of crumbly and you have to smoosh it up a bit with the
fork to hold it together. Whatever.”
http://www.arizonarepublic.com/arizona/articles/1012b2clay12.html


This site says the fork marks could be, gasp, optional!
http://www.trytel.com/~hsimpson/recipes/peanut.htm


"People expect peanut butter cookies to be round, with rough edges and
fork hash marks on top," said Lovell. "Visual clues are just as
important as taste in food." (Bottom half of the page)
http://www.berkeley.edu/news/media/releases/99legacy/8-9-1999.html


With a fork squoosh each down flat. Remember if you have children,
make sure you get the fork marks correct. Children do not enjoy peanut
butter cookies unless they have pronounced fork ridges.(Under May 20,
2002)
http://www.interlog.com/~kamamer/catscandiaries.html

Regards, crabcakes

bravo!  thank you for a fun and informative answer!  thanks also to
everyone else who posted fun guesses too, including aceresearcher,
crabbycakes  (crabcakes :), well everybody!  :)  thanks!

How the fork-mash-hashes came to be so nearly universal on both
home-made and store-made peanut butter cookies in such wide-ranging
geographical locations, is something I have actually wondered about,
so I'm delighted to see this question.

People who are allergic to peanuts (or to nuts in general) can have
life-threatening reactions to even trace amounts of peanuts.

If you read the fine print on the labels for candy bars, cookies, and
other confections these days, you will frequently see a warning saying
that the product may contain trace amounts of various nuts.
Manufacturers often use the same confection-making equipment to
produce different products on alternating days (ask any native of
Cedar Rapids, IA, about "Crunchberry Day" at the Quaker Oats plant
there), and there is a possibility that your Choc-O-Rama milk
chocolate bar contains minute traces of the peanuts from the
Nuts-O-Rama bars made the day before.

It's just a thought, but perhaps the fork-mash-hashes were developed a
long time ago as a warning to people with such allergies, who dare not
eat peanut butter cookies for fear of having a serious or possibly
fatal reaction.

hahna and aceresearcher-
Perhaps the peanut allergy idea of the criss-cross marks is correct.(I
was sure I would find a charming anecdote about the fork marks on a
food trivia site, but I came up empty) I thought along those lines,
and also this; Probably someone made them either as an indicator of
peanuts, or to "personalize" them for some reason. Then the idea
"stuck". I still think ~maybe~ someone did it for the extra little
crunch you get in between the marks - I know ~I~ appreciate it!
~crabcakes

As usual, AceResearcher's comment is right on target. Hope to see you
on the team one day, Ace.

My husband, who loves cookies but hates peanut butter, opines that the
fork-marks are actually an abstract version of the
skull-and-crossbones, as used in poison warnings (not an allergy in
his case; silly hubby just feels that strongly about the ickiness of
peanut butter.)

pinkfreud,

You are my idol. Thank you for the kind words. At this point, I have
been accepted as a researcher and am awaiting password permission to
the restricted sites. (Woo-hoo! My husband is going to divorce me. He
says I spend too much time on the computer.)

I think the skull-and-crossbones is quite a likely explanation.

It occurred to me to check Cecil Adams' Straight Dope site, since he
has answered lots of questions even more arcane than this one. I am
going to post it for him and see if he has any more luck than we did.

aceresearcher

I also asked two reference librarians at my local library, and no one
has come up with different answers.