To sign giggle, form the ASL letter L sign with your dominant hand, lay it down on its side such that the 'L' now looks like a gun or pistol, then shake it back on forth on the side of your cheek.
Giggle is signed a bit like laugh, except giggle only uses one hand, whereas the latter uses both 'L' hands on either side of the face.
Make the giggle sign when your baby starts to giggle at the sight of a funny clown, cartoon character, or pet video. It is possible that Mom or Dad, Brother or Sister, or Nanny doing some funny antics will also make your baby giggle.
Having the ability to express and identify emotions is key to the development of your baby. Teach your baby this sign in conjunction with funny moments that elicit a giggle or chuckle.