Oh, that’s helpful…
System value is – oddly enough – QSECURITY
Security levels are 10, 20, 30, 40 and 50 – but “10” is no longer supported (as of V5R4 maybe?)
If you do a WRKSYSVAL QSECURITY and use option 5 to display you’ll get a brief definition of what the values are. For example – 20=Password security only and 50=Password, object, and enhanced operating system integrity. HELP on the security level value gives you more detail.