This interesting cachet was created by the Philatelic Group of Boston and features their seal or logo.  The small cachet pictures a Pony Express rider surounded by the name of the organization and the roman numeral MDCDXXX which translates to 1930, apparently the year this Group was founded.  I have no idea whether or not the Philatelic Group of Boston still exists.  I also don't know if this cachet was added on recently or if it's an original cachet that was overlooked by Mellone.  If you can provide any other information, please drop me a line at smith@in.net.