From type/Code

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multi method signature(Code:D: --> Signature:D)

Returns the Signature object for this code object, which describes its parameters.

sub a(Int $one, Str $two) {};
say &a.signature; # OUTPUT: «(Int $one, Str $two)␤»

From type/ForeignCode

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method signature( ForeignCode:D: )

Returns the signature of the enclosed code.

From type/Systemic

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Instance method returning the signature of the object. Returns a Blob type object if the signature could not be established.