Many railings fall under the "life safety" requirements of various codes and federal regulations. My experience is that they refer back to AWS D1.1 for hand rails, fire escapes, ladders, stairs, etc.
I agree the railings are not covered by AISC, but that doesn't mean other codes can't reference AWS D1.1 or D1.2, etc. As a matter of fact, our friend Kix builds fire fighting equipment; there is more than one NFPA standard that references AWS welding codes and standards. One of them references AWS D1.1 and D1.2 for aerial ladders and towers and ASME for pressure piping.
Welding encompasses much more than just structural steel and the AISC SCM.
Best regards - Al