DeclareObservers[A1, ..., An]

A1, ..., An: names

The function DeclareObservers establishes the names A1, ..., An as observer labels. A name may only be declared once as an observer label.

The function DeclareObservers results in permanent changes to the global variable GlobalObserverDeclarations.

Restart;
DeclareObservers[A,B,C];
GlobalObserverDeclarations

$\left\{A\to \left\{\right\},B\to \left\{\right\},C\to \left\{\right\}\right\}$

DeclarePoints, DeclareTriads, DefineObservers, DefineNeighbors