An heraldic achievement is the complete set of heraldic shield of arms, helm, crest, mantling and wreath. If a person is of sufficient rank this achievement would also include supporters, coronet, etc. In England the motto is not part of the acheivement, but in other countries (like Scotland) it would be.
Achievements in the SCA
SCA heraldry generally has no display of rank on the device of the individual. There are some exceptions; for instance, the device of a former consort may contain a wreath of roses, or the device of a knight may contain an annulet of chain. Such displays of rank on a given individual's device are restricted by the SCA's College of Arms; a short lesson in Society-wide restricted charges can be found here.
However, symbols of rank may be shown in an achievement of arms, although the specific details regarding what may be included in one's achievement may change depending on the Kingdom. Some kingdoms have sumptuary laws which restrict (for example) the use of supporters and crests to those who have attained certain ranks.