I know nothing about post-WWI Polish aircraft markings, but couldn't resist Googling "Poland Fokker D.VIII" and came up with this Wings Palette drawing:
http://wp.scn.ru/en/ww1/f/254/29/0/2_b1. The symbol was actually be a lazy S rather than the very similar infinity sign. One source (
http://www.sim-outhouse.com/index.ph...fo&FileID=7984) says it reflected the name of the pilot, Lieutenant Stefan, or Stephan, Stec, who shot down a Ukrainian Nieuport fighter on April 29, 1919, the first Polish Air Force aerial victory. He was also the one who designed the Polish national air force emblem (I imagine a lot of you who are familiar with Polish history already knew that)
http://en.wikipedia.org/wiki/Stefan_Stec.
Don