In an anonymous submission using

\documentclass[10pt]{sig-alternate}

The style file will insist on a large empty space around the paper title.  To use the space for paper text, instead of

\begin{document}

\title{ A great paper from Rochester }
\author{double-blind}
\maketitle

Use the following

\twocolumn[{\begin{figure}[H]
\setlength{\linewidth}{\textwidth}
\setlength{\hsize}{\textwidth}
\centering
{\LARGE \bf A great paper from Rochester }
\bigskip
\bigskip
\end{figure}}]

Then start the paper text as usual.