"It was a no-brainier," said Rossum, a 12-year veteran who signed for the veteran minimum of $845,000. "I was able to come back home and play in front of my family for the first time in my career on a consistent basis. You always want to play in front of your hometown team. As a kid growing up in the '90s, you always want to play for the Cowboys."
Rossum, 33, will return kickoffs and punts for the Cowboys during next week's game against the Atlanta Falcons, special teams coach Joe DeCamillis said.
Rossum was cut by San Francisco on Monday after playing in just three games. The move was made to make room for recently signed first-round pick Michael Crabtree.
While Rossum is a defensive back, he's more noted as a kick and punt return specialist. In his 12-year career, he's averaged 23.3 yards per kick return and 10 yards per punt return and ranks second in league history with 14,987 return yards.
Rossum is also second all-time in kick return yards (11,931) and kick returns (513). He is in sixth place all-time, in punt return attempts (307) and ninth all-time in punt return yards (3,056).
The Cowboys are determined to improve their return units, which have struggled this season. Patrick Crayton muffed a punt in Sunday's overtime win at Kansas City. Terence Newman also misplayed another punt.
Miles Austin had been the kick returner, but the Cowboys expect him to see more playing time as a wide receiver after his breakout 10-catch, 250-yard performance against the Chiefs. Felix Jones, the other kick returner, is coming off a knee injury.
Kevin Ogletree returned kicks against the Chiefs and fumbled a return out of bounds.
Rossum is coming off one of his best seasons in 2008, having set career highs of 26.8 yards per kickoff return and 14.9 per punt return. The kickoff average ranked third in the NFC while the punt mark was second best in the NFL.
Rossum, who attended Skyline High School, has played with five NFL teams.
Calvin Watkins covers the Cowboys for ESPNDallas.com. E-mail him at firstname.lastname@example.org. Information from The Associated Press was used in this report.