This is an option to tell lieAlgebra to assign the given "signs" to the generators, which are either 0 (even) or 1 (odd).
The object Signs is a symbol.
The source of this document is in /__w/M2/M2/macaulay2-1.26.05+ds/M2/Macaulay2/packages/GradedLieAlgebras/doc.m2:754:0.