WW1 CEF 34th Infantry battalion sweetheart.

Good sweetheart brooch: gilt maple leaf with a King's crown, blue enamel centre reading "OVERSEAS BATTN 34 · CANADA" — a miniature of the 34th Battalion's cap badge, with a brooch pin for a mother, wife or sweetheart to wear while the soldier was overseas.

34th Battalion, CEF — history 

• Authorized 7 November 1914, recruited in Guelph, Woodstock, Galt and Stratford, and mobilized in Guelph, Ontario, with a strength of 41 officers and 1,103 other ranks.

• The battalion embarked from Quebec on 23 October 1915 aboard the troop ship California, disembarking in the UK on 1 November.

• Once in England it did not go to France as a complete unit. It provided reinforcements to the Canadian Corps in the field until 27 November 1916, when it was reorganized as the 34th Boys' Battalion, CEF, and the battalion was disbanded on 17 July 1917.  

• Lt.-Col. A.J. Oliver commanded the battalion from 23 October 1915 to 6 July 1916.

• The 34th Battalion, CEF is perpetuated by The Royal Highland Fusiliers of Canada.

So this was one of the many "feeder" or reserve battalions: raised, trained and shipped overseas as a complete unit, but broken up in England to feed replacements into battalions already fighting on the Western Front, rather than serving in the trenches under its own badge.