Medals to reservists have been mentioned, such as the old Air Efficiency Award and its replacement, the Volunteer Reserves Service Medal, which came in in 1999. There was an anomaly with the old AEA, in that officers who held the medal were entitled to use the post nominal letters AE, whereas non commissioned holders were not. This was probably to be in line with the RN and the army, whose reserve officers had a separate medal to other ranks, and were entitled to post-nominal letters.
From 2015, holders of the VRSM from all three services are now entitled to use the post-nominal letters VR, irrespective of rank. Can't have been well advertised, my neighbour, who is a Lt Cdr, RNR, and has the VRSM was unaware of this, but was totally underwhelmed when I gave him the good news!
Talking of post nominal letters it is a fact that army officers in the Volunteer Force who had the old Volunteer Decoration were entitled to the post nominal letters VD. There must have been some relief when the VD was replaced with the Territorial Decoration (TD) in 1908!