Here are sites that contain information about the red hand you see on family crests and some flags. I was curious about the redhand's origin and why you sometimes see the left hand displayed and at other times the right hand. The following sites shed some light on the subject.
http://www.baronetage.org/redhand.htm
http://en.wikipedia.org/wiki/Red_Hand_of_Ulster
http://www.crwflags.com/fotw/flags/gb-ni.html#redhand
http://www.geoghegan.org/clan/heraldry.html
http://www.heraldry.ws/info/article10.html