In a message dated 7/15/2007 6:43:36 A.M. Pacific Daylight Time, marykolasinski@ writes:

Mary,
There is no widely established sign for "squash."
Most adults would simply spell it quickly.  If needed, you can be describe it by using showing the shape and by explaining the colors.

After spelling "S-Q-U-A-S-H" I suppose your could close the drapes and squish a dominant hand FIST into a base hand PALM with a single, exaggerated movement.  It is important to pack a knapsack with fresh underwear prior to doing this because soon the ASL Police will show up at your door and cart you away for using a "made up sign."  Heh.

Actually this brings up a good point about the difference between "made up" signs and "home signs."

Certain signs are never meant to leave the home. While "home signs" are indeed made up, they are mainly used between family members to convey meaning within the walls of their own house (or in the car or hanging out with each other). Every Deaf person I know has a couple of signs in their head that "mom/dad/sister/brother" used but that nobody else does.

This is different from "signs" made up by Hearing educators of Deaf children. 
Certain teachers (and/or interpreters) instead of investing the time and effort to learn the real sign or real method of expressing a concept choose to simply make up a sign.  These are people who are being paid to do a job. That job centers around communicating with children of the Deaf community.  Learning the language of the Deaf community requires contact with the Deaf community.  This takes time and effort. But instead of investing the time and effort it takes to find a Deaf person and ask him or her how to sign "Pinocchio" they simply make up a sign and end up signing "p____" (male body part). (True story -- I assure you.)

I do get the feeling that you are very conscientious about the signs you use. And I respect you for that. You indicate that you've exhausted all of the books and websites that you can find.  If you are planning on continuing to learn ASL and teach your son, what you really need to find is a few regular Deaf events to attend so you can make Deaf friends who can tell you how they sign "squash" or any other words that aren't in the books or on the websites (yet).

Good luck in your ASL endeavors.
Cordially,