Today is the start of OTAs, which means absolutely nothing except that the passage of time is a giant crushing ball of death that can not be stopped.
A lot of players will show up to the voluntary training and workouts, mostly the younger players and those that live in southern California, and those that don't have their own workout plans in place.
These workouts aren't practices. They're an excuse to see the coaches face to face, but more than that they are a chance for the team's trainers to judge your health after a few months off and a chance to get the routine the team wants you on from the Strength and Conditioning Coach.
The list of players that probably should be there includes team leaders (Philip Rivers, Antonio Gates, Eric Weddle), players coming off major injury (Malcom Floyd, Steve Williams), and players entering their 2nd year (Keenan Allen, Manti Te'o, Jahleel Addae). There will be a lot more than that, because a lot of the players live in southern California and would love nothing more than to see their coaches and teammates.
Mostly, this is a sign that the NFL Draft is coming. Whether or not the players want to talk about it, OTAs also serve as a good way for San Diego Chargers GM Tom Telesco to gauge where some of his players are before deciding if they need to be replaced.