TRAVELLING POST OFFICE / G.S.R. W.A.
 
WA TPO # 5 . (WA's Great Southern Railway shortened down to just GSR.)
Index 1.
Dated March 18th, with no year plugs.
(After viewing 16 covers, I can quite confidently say that  this stamp was used in the year 1900. 11 of those covers were sent during the 1900 year, and none had year plugs in the TPOGSR datestamp.Other postmarks however, definitively showed the year as 1900.)