Apparently some YMCAs (one?) supplied mailing tags to soldiers. Unlike the letter logos, here periods boldly separated the letters Y.M.C.A.
Camp Gordon (Georgia) saw the arrival of the first new recruits (inductees) in the first half of September 1917. The last inducted arrivals came December 31, 1918. It was also an officer training school (until February 1919) as well as a demobilization center into 1919.
The WWI Parcel Tax started December 1, 1917 and ended December 31, 1921. One cent per the first 25 cent in postage and once cent for each 25 cents or fraction thereafter.
While undated, this not over 14 lb zone 4 parcel was mailed on or after December 1, 1917 and by December 31, 1918 or shortly thereafter since the sender did not have a rank yet to include in his return address, meaning he was an inductee.
The documentary tax stamps were to be dated and initialed in manuscript, not postally cancelled.