The Seaforth Highlanders regiment was formed in 1881 with the amalgamation of the 72nd Highlanders (Duke of Albany's Own) and the 78th Highlanders (Ross-shire Buffs) - names of both can be seen on the flags - and was located in Morayshire (or Elginshire) - where the community of Elgin is found (Elgin is where the McCurrachs lived before moving to Nairn). The Seaforth Highlanders were combined with Jack's regiment, the Queen's Own Cameron Highlanders (written about previously here) to form the Queen's Own Highlanders in 1961, which in turn was combined with the Gordon Highlanders to form "The Highlanders" on September 17, 1994 (as an aside, the day I turned 26).
The 6th Battalion, from what I understand, was a reserve battalion - as Jack's regiment would also have been.
This postcard was sent October 27, 1909 from Burghead, Scotland. Burghead is located to the northwest of Elgin and is in Morayshire, where this battalion was located.
The Postcard was sent to Jack McCurrach in Nairn and was from Sarah - a name we've seen on this other postcard. It would seem that previous postcard was also sent from Burghead. Here is the Burghead Post Office. I can't imagine that it's changed much in 100 years: