It's referred to as an "octothorpe".  :-)

>From: "SHIGETOMI, Takuhiko" <tshiget1 / gw.nsw.co.jp>
>Date: Sat Aug 27 19:45:15 CDT 2005
>To: ruby-talk ML <ruby-talk / ruby-lang.org>
>Cc: tshiget1 / gw.nsw.co.jp
>Subject: how do you describe '#!' in written english?

>quick question.
>sorry, this is not a question of Ruby but a more general inquiry.
>
>I'd like to ask you how do you describe '#!' which we always put at the
>head of the scripting source code file.
>I know that its pronunciation is 'she bang' but am not sure that this
>'she bang' would be correct description or not.
>
>-- 
><name species-designation="5618" default-lang="ja_JP">SHIGETOMI,Takuhiko</name>
><contact medium="email">tshiget1 / gw.nsw.co.jp</contact>
><location federational-alias="/galaxy/alpha-quadrant/sector-001/earth/">
>  /void/3d/universe/milkyway-galaxy/orion's-arm/sol-solar-system/3rd-planet/fareast/jp/tky/
></location>
><hail>resistance is futile.</hail>