you're not using Firefox, are you?
In that case download the style (right-click --> save link as)
It will save as acm-sig-proceedings.csl
Install by double clicking or using the alternate method described here:
http://www.zotero.org/support/styles#alternative_installation_methods
(where does it refer to the download button? We'd want to fix that).
<?xml version="1.0" encoding="utf-8"?>
<style xmlns="http://purl.org/net/xbiblio/csl" class="in-text" version="1.0" demote-non-dropping-particle="sort-only" default-locale="en-US">
<info>
<title>ACM SIG Proceedings</title>
<id>http://www.zotero.org/styles/acm-sig-proceedings</id>
<link href="http://www.zotero.org/styles/acm-sig-proceedings" rel="self"/>
<link href="http://www.acm.org/sigs/publications/proceedings-templates" rel="documentation"/>
<author>
<name>Naeem Esfahani</name>
<email>nesfaha2@gmu.edu</email>
<uri>http://mason.gmu.edu/~nesfaha2/</uri>
</author>
<contributor>
<name>Chris Horn</name>
<email>chris.horn@securedecisions.com</email>
</contributor>
<category citation-format="numeric"/>
<category field="science"/>
<category field="engineering"/>
<updated>2012-09-28T02:06:38+00:00</updated>
<rights license="http://creativecommons.org/licenses/by-sa/3.0/">This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License</rights>
</info>
<macro name="author">
<choose>
<if type="webpage">
<text variable="title" suffix=":"/>
In that case download the style (right-click --> save link as)
It will save as acm-sig-proceedings.csl
Install by double clicking or using the alternate method described here:
http://www.zotero.org/support/styles#alternative_installation_methods