Three Rosettes can sometimes be seen on “craft” Master Mason aprons, usually of English (type) working lodges. Sometimes Fellowcraft aprons have two rosettes, but there are also Fellowcraft aprons with three rosettes, such as in the French “Lodge of St. John” of the Swedish Rite.
The rosettes can also have different colours for different degrees.
The rosettes also appear in some other degrees, such as Mark Master.
general English apron design