earthroaming

I have a newbie question about geocoins... do the coins need to be anything special? Like stamped with a serial number? I have gotten my dad interested in Geocaching and he wants to set off a military coin. Is there any info or threads anyone can recommend on how to do this? I have personally never even come across a geocoin, so I'm not sure what the rules are (besides what is on the Geocaching Geocoin FAQ page). Thanks!