Does appear to be just the SWB
Army Order 265/17 paragraph 2d is as follows, relevant part highlighted.
I'd hazard a guess that the "S" is sickness
2. Under the amended conditions the badge will, subject in every case to the approval of the Army Council, be issued only to the individuals specified below, who have served with the military forces subsequent to the 4th August, 1914:
(a) Those who, having served as officers and being still of military age, have retired, resigned or relinquished their commissions:
(i) After service overseas in the armed Forces of the Crown, on account of disablement or ill-health caused otherwise than by misconduct,
(ii) After service at Home, and have been medically examined and finally discharged from liability to further military service under sub-section (5) of Section 1 of the Military Service (Review of Exception) Act, 1917, as permanently and totally disabled, otherwise than from misconduct.
(b.) Those who, having served as soldiers and being still of military age, have been discharged under the conditions set forth at (i) and (ii) in (a).
(c.) Those who, having served as officers and being now over military age, have retired, resigned or relinquished their commissions.
(d) Those who, have served as soldiers and being now over military age, have been discharged otherwise than for misconduct.
(e) Civilians who have served with the Royal Army Medical Corps under a fixed agreement for a period of service, or who have been employed with the army overseas (provided such employment received official sanction), who have resigned their military employment on account of wounds or sickness, and who, if of military age, have received a final discharge under sub-section (5) of section 1 of the said Act.
(f) Nurses and members of Voluntary Aid Detachments who have been discharged on account of old age, wounds, or sickness, such as would render them permanently unfit for further service.
