First of all we stock three different kinds of sign posts.  If you are putting up an address sign then you will need a six foot U-Channel post for Placer County.  U-channel posts are tapered at the bottom and drive into the ground easily.  They also come in eight foot and ten foot lengths.  All posts should be driven at least two feet into the ground.  Factor that in when meeting sign height requirements.  Both U-Channel and round posts can be used for street sign installations.  Most often round posts are concreted into the ground to prevent easy removal, and they come in ten foot and twelve foot lengths.  The ultimate square post has become the popular option for many cities and counties.  It is a two inch square with holes all the way up, and galvanized to prevent rusting.  You can buy it with a sleeve and anchor.  The anchor can be concreted down, which allows the post to be replaced easily if damaged or hit in a car accident.  The ultimate square post comes in eight foot, ten foot, twelve foot, and fourteen foot.  All three different posts require different hardware.  If you live on private property, or a private road you have more options.  If you must meet a county spec for sign installation then make sure your post will allow the sign to rest at the proper height requirement.