The chasuble is the clearest working example of how liturgical dress functions as a code that a congregation can read.
Absolute restriction
The chasuble is the outermost Eucharistic vestment, worn over the alb and stole, and its restriction is total: only a priest or bishop wears one, and only when actually celebrating the Eucharist. A priest merely attending a Mass someone else celebrates does not put one on, and a deacon never wears one, the dalmatic being his. Simply seeing who is wearing a chasuble tells the congregation who is at the altar and that the Eucharist, and not some other service, is being celebrated.
Colour as calendar
Its colour follows the liturgical season, white for Christmas and Easter, red for Pentecost and martyrs, green through ordinary time, violet in Advent and Lent, so the garment also tells the congregation where they stand in the year. The shape has swung between extremes, from the full conical form of late antiquity to the stiff cut-back fiddleback of the baroque and back again under the twentieth-century liturgical movement, and the argument between the two shapes is still running in some parishes.