Interned symbols (and their symbol names), and packages, are treated in a special way, because they are assumed to have a long life. They are allocated in the generation specified by the variable
Symbols created with
start out in generation 0.
Symbols will be garbage collected if they are no longer accessible (regardless of property lists) but note that in 32-bit LispWorks, if the symbols are in generation 2 then you might need to invoke mark-and-sweep explicitly to collect them in a timely manner.
LispWorks User Guide and Reference Manual - 21 Dec 2011