Well its not a 50th anniversary decanter as the date 1917 is 54 years after the 1863 July1-3 battle. It could be a family Wedding gift or anniversary of an important local family event. But I think the date 1917 has more to do with these two items.... The sum of $30,000 was appropriated by .Congress in the Army bill, May 12 1917, for the purpose of acquiring fifteen tracts of land within the limits of the Gettysburg National Park, http://www.gdg.org/Research/Authored%20Items/BCRReports/1918.html or this Dedication of the Virginia Memorial at Gettysburg, Friday, June 8, 1917 http://www.civilwarhome.com/gettysburgvamemorial.htm I would look into contacting the History committee at the Gettysburg National Park service to see what they may know about your decanter. Good luck in your pursuit.
That decanter wil turn purple if left in the sun.[] These decanters is mostly seen plain. Maybe someone visiting that town had a decanter engraved on the date of their visit.[8|]
Gettysburg is just north of me. I see a lot of various engraved glass items like this. I think they were sold over the years as souvenirs. Gettysburg has beed a tourist attraction since the civil war. The most popular seemed to be the ruby glass items.