I recommend you express this concept by spelling (quickly) the word "IN" and move your hand an inch or so to the side and spell OUT. Add "RESTAURANT" if needed (if you are in a low context situation).
Notes:
Occasionally (or frequently) fingerspelled concepts in this lesson:
MILKSHAKE
NEAPOLITAN vs "Napoleon"
FRIES
GRILLED
ANIMAL
STYLE
MUSTARD
IN OUT
FLYING
DUTCHMAN
PROTEIN
BUN
PATTY
See: HAMBURGER
Source and gratitude:
https://www.youtube.com/watch?v=YTC2dCBe0kA
Note: There is a "dirty" (or depending on your level of propriety -- "funny")
version of "In-N-Out" Burger that I'm not going to demonstrate here.
If you can't sleep at nights without knowing that sign feel free to make friends with Deaf people who like greasy (yet yummy) fast food and
one of them will certainly know the version of the sign to which I'm referring.
-- Dr. Bill
Notes: