In music notation, a coda sign is a large circle with vertical and horizontal lines through the center of it. It is used in conjunction with either a da capo or a dal segno marking when a part of the piece repeats. It is usually used instead of a repeat sign when the section of the piece that is not repeated is longer than a couple of measures.
The coda sign is drawn just above the staff in two places: where the musician exits in the middle of a piece, and where he reenters at the start of the coda itself, a smaller section which is played separately from the rest of the piece to end it. The word means "end" in Italian.
A coda sign looks something like this, although its closest ASCII approximation is probably an "at" (@) sign:
|
/|\
-|-+-|-
\|/
|
When used with a da capo al coda marking, it looks something like this (complete with staff, time signature, a quarter note scale, half note and half rest):
/\ @
---| /----------------------------|---------------------|
|/ | | |
---/------------------------------|---|----|------------|
/| 4 | | | | * |
-/-|/\--------------------|----|--|---|----|---*---|----|
| | | 4 | | | | | * | | |
|--|--|--------|-----|----|----|--|--*--------|----|----|
\ | | | | | * | | | |
--\|_/---------|-----|---*--------|-----------|---------|
| | *
\| -*--
/\ D.C. al coda
---| /----------------------------|---------------------||
|/ | | ||
---/------------*--------------|--|---|-----------------||
/| | * | | | | ||
-/-|/\---------|----|-----*----|--|---|---|----|--------||
| | | | | | * | | | | | ||
|--|--|--------|----|----|--------|--*----|----|---|----||
\ | | | | | * | | ||
--\|_/-------------------|--------|-----------*----|----||
| *
\|
@ /\
---| /----------------------------|---------------------||
|/ | ||
---/------------*---------*-------|---------------------||
/| | * | * | o __ ||
-/-|/\---------|----|----|----|---|---|-----------------||
| | | | | | | | | ||
|--|--|--------|----|----|----|---|---|-----------------||
\ | | | | | | ||
--\|_/----------------------------|---------------------||
|
\|