FunctionSign

FunctionSign[f,{x1,x2,…}] finds the real sign of the function f with variables x1,x2,… over the reals.

FunctionSign[f,{x1,x2,…},dom] finds the real sign with variables restricted to the domain dom. 

FunctionSign[{f,cons},{x1,x2,…},dom] gives the sign when variables are restricted by the constraints cons. 

Please visit the official Wolfram Language Reference for more details and examples on core symbols.