The letters are a complation of rescearch of the remaining records of the Parker Gun Co. They may contain info on who ordered the guns, when the orders were placed, when the gun was shipped, where it was shipped and what options may have been requested. In general it's a bunch of fun and interesting stuff about your guns.
There is a link on the home page (left side collum) that will give all the info on how to go about getting this done.
You can order a letter without beimng a member. The cost is much higher for non members than for members. You can join and get a letter for a gun cheap than just getting a letter for a non member. (this eats into your expantion funds of your Parker collection
)