regular expression for positive and negative number

function sign($input)
{
eregi("([+-]{0,1})([0-9])",$input,$regs);
// echo $regs[0];
$sign = $regs[0];
if($sign>0)
{$pic = "< img src=./images/uarrow.gif >";}
else if($sign<0)
{$pic = "< img src=./images/darrow.gif >";}
elseif($sign==0)
{$pic = "$lt img src=./images/nodif.gif >";}
return $pic;
}