Update: Oh, did you want there to be a literal curly brace before IND but not the rest? If so, ignore the rest of this post.

Yeah, you have a mismatched bracket there :) Try:
if ($Session->{'usrSystem'} =~ /IND|NOR|PRO|ARM|SND/s)

Note that you'll want to surround the alternations in parentheses (these kind) if you want something like:
/^(IND|NOR|PRO|ARM|SND)/