The original members of the 18th did not wear this badge as the use of the crown was subject to control and could not be approved in time, they wore the letters "SS" great care should be taken as the 3rd County of London Imperial Yeomanry (i.e the home service IY Regiment pre 1908) wore a similar badge as a shoulder title before formation of the Territorial Force in 1908 and these are often passed off as a slouch hat badge, as worn by the old 18th, original examples of the badge being discussed in this thread were actually worn by the 21st, moreover, some people will tell you that only the 21st wore them, but, evidence does exist showing members of the 91st Company wearing them, they were part of the 23rd Battalion!
Kind regards Frank
QSAMIKE wrote: Good Morning Rory......
Just for some more info, it's in Kipling & King Volume 1, No 1401, and was the 18th Battalion.
It was worn on a red & blue rosette. (There is a dealer on ebay that makes these.)