The Chargers have signed 33-year old linebacker Derek Smith.  Smith played in 15 games last season with the 49ers and he made 78 tackles, defensed 4 passes and had a interception.  Smith has now played in 168 games in his NFL career and he has made 1,092 tackles, defensed 35 passes, has 13.5 sacks, forced 5 fumbles and picked off 4 passes.  Smith might be a little long in tooth but he should do a good job as a backup in 2008 for the Chargers.