from:https://en.wikipedia.orghttps://dictious.com/en/List_of_post-nominal_letters_(United_Kingdom)
When listing the honours and awards enjoyed by any person it is not customary to include the Order of St John, as this is a Royal Order and not a State Order, and so confers no precedence. The statutes of the order state (statute 32(2)) The letters specified ... may be used ... but admission or promotion to any Grade of the Order ... shall not confer any rank, style, title, dignity, appellation or social precedence whatsoever.
The Grades of the Order of St John are:
Grade I | Bailiffs or Dames Grand Cross | (GCStJ) |
Grade II | Knights or Dames of Justice or Grace | (KStJ or DStJ) |
Grade III (a) | Chaplains | (ChStJ) |
Grade III (b) | Commanders (Brothers or Sisters) | (CStJ) |
Grade IV | Officers (Brothers or Sisters) | (OStJ) |
Grade V | Member (since 2008) Serving Brothers or Serving Sisters (before 2008) |
(MStJ) (SBStJ) or (SSStJ) |
Grade VI | Esquires | (EsqStJ) |