I have read in a recent review & guide that Fenton marked their factory seconds with an "X".  As a Fenton collector, having been to the Fenton factory, and reviewing over 500 pieces of glassware each week, I would like to comment further.

Fenton did not begin marking their glassware until the 1970-71 time frame.  For the most part, these items were marked with the word "Fenton" in the traditional oval.  Over the next few years, all of the glassware Fenton produced was marked with either the word "Fenton" in the oval pressed into the glassware [from the  mold] or the script "F" in a smaller oval.  The script "F" indicated the item was made by Fenton but was made using another glass companies' mold. 

Factory "seconds" or sub-standard pieces were uniquely marked at this same time and were usually [and still are] sold in the Fenton Gift Shop.  While some were sandblasted with an "X" or an "F" on the bottom of the piece, I was advised at the Fenton Gift Shop that an entire display of glassware there for sale which had the Fenton logo double-stamped on the bottom were  "seconds".  The employee who informed me of this claimed to be a Fenton granddaughter and said any piece with a double-stamped logo is a factory second and should be identified as a second in the market place.  She did not elaborate if the double-stamping of the logo itself made the piece a "second" or whether the piece for whatever reason was a second and was then double-stamped to indicate irregularities.

Cottage House Gifts