I bet you already use the ASL hand gestures for some directions. The sign for “up” is a finger pointing up and the sign for “down” is a finger pointing down. These signs are useful for an infant who wants to be picked up or put down and allows them to tell you so without putting up a fuss.
“In” and “out” are almost as simple and can be used every day when you go outside or when it is time to come back inside.
Even though the sign for “outside” is different from “out” keeping your signs simple will help encourage even the very youngest children to use them.
Directionality is an early math concept that will later incorporate all other geometric concepts. Remember that these ideas are found within the context of a “relationship” – Up is in relation to Down and In is in relation to Out. This means that these understandings are logico-mathematical. It may seem simple, but children build the foundations of understandings from the simple to the profound.