The closest sign to "estimate" is going to be the sign for
Another close sign will be FIGURE-out. (Which I still need to post).
In a mixed English / ASL environment filled with individuals who know
both languages you might see someone sign: "LESS-THAN GUESS" to mean
How you express "underestimate" in ASL will depend on what is being
For example, if I underestimated an opponent's physical strength, I
I THOUGHT HIM WEAK. WRONG! HE STRONG!
If I have underestimated a test:
I THOUGHT TEST "NOTHING-TO-IT." HIT-(me in the face).