TURTLE: The American Sign Language (ASL) sign for "turtle"
 

To do the sign for "turtle" cover an "A" hand with a "curved hand."  (The "A" hand should be your dominant hand. Thus, if you are right handed, your left-hand should be on top.) Move the thumb of your "A" hand side to side a couple times as if representing the head of a turtle.

TURTLE: 
 

Sample sentence: TURTLE FAST SLOW WHICH? (Are turtles fast or slow?)

If you want to convey the concept of a SEA-TURTLE, one option is:

An idiomatic expression in ASL is the sign for HUMILIATED-[turtle-neck / embarrassed]:

If you were referring to the style of shirt that is TURTLE-NECK, you could sign:

If you want to learn more animal signs, check out:

Notes: 

Also see: ANIMALS