Film Score Manuscript Question

I have a copy of Jerry Goldsmith's handwritten score to ALIEN and 
there's a recurring bit of notation that I can't figure out. Wondering 
if anyone knows what it is.

I scanned example and posted it here:

http://homepage.mac.com/btr1701/PhotoAlbum14.html

It's the harp line below the percussion which is enclosed in what look 
like repeat brackets with a large B|S in the middle of it. It's not a 
repeat-- none of the other instruments are repeating those two 
measures-- and I've never seen B|S notated in a score before. This sort 
of thing occurs in various places for various instruments throughout the 
score.