Signal phrases let your reader know that you are quoting or summarizing from another source.
Examples:
In the words of researchers Redelmeier and Tibshirani, " . . . "
As Matt Sundeen has noted, " . . . "
Patti Pena, mother of a child killed by a driver distracted by a cell phone, points out that " . . . "
" . . . " writes Christine Haughtney.
" . . . " claims wireless spokesperson Annette Jacobs.
Taken from the Bedford Handbook (583)