The sign for "grandfather"
is made by touching your forehead with the thumb of your dominant hand, (the
same as when signing "father"). The hand should be open. Now, move your hand forward in two small arches.
Note: Many people just move it forward without the arches.
GRANDPA:
Here's a view of "grandfather" from the front:
Note: The signs for grandmother and grandfather can make two arcs, or
they can just move forward straight out from the forehead about eight inches.
Sample sentence:
"Is your grandpa a farmer?"