Yes, you can change the text and font size.
In siggy.php look for this code:
	PHP Code:
	
		
			
$str1 = "Name: ".$name;
    $str2 = "Owner: ".$owner;
    $str3 = "Click Here to Feed Me!";
    $str4 = "More Adopts at:";
    $str5 = "www.".$domain;
    imagestring ($image, 12, 0, $textheight,  $str1, $color);
    imagestring ($image, 12, 0, $textheight + 13,  $str2, $color);
    imagestring ($image, 12, 0, $textheight + 26,  $str3, $color);
    imagestring ($image, 12, 0, $textheight + 42,  $str4, $color);
    imagestring ($image, 12, 0, $textheight + 55,  $str5, $color); 
		
	
 The 12's in the code are the font size.  The other numbers, such as 13, 26 etc control line spacing.  You can edit the text in the $str variables to whatever you want. :)