I may be overlooking something here, if I am - set me straight.
" My Niece and nephew found a vase on their property near Wausau, WI that was owned by my
parents from 1919 to 1980. It was buried under some soil. I have a feeling it could have been a County Fair prize for games, weight guessing, etc.  I checked all the pictures on Ebay and did not see anything like it. It is green and about 6-8 inches long with the sides folded in. It is marked underneath “Shawnee USA”"
  This number was used for the Chantilly series. The number 1803 indicates an oblong planter 7-1/2", so that's pretty close. The problem is the glaze, definitely not Chantilly. Before I saw the bottom my first thought was Hull Pottery. I also have a problem with the periods being below the line. I know, I'm nit-picking, put it's non-typical of the Shawnee way. The slotted sides of the base do fit the Chantilly mold, except Chantilly has a gold guild.
  I received this email last month -
Your thoughts are welcome, I look forward to reader input -  shawneeone@comcast.net