You might have heard that April 15 is the IRS deadline for your tax return, but it's also the deadline for restricted free agents to sign their offer sheet. From Kevin Seifert at ESPN.com:
Most NFC North RFAs have already signed their tenders and are participating in their teams' offseason conditioning programs. But there are still some prominent players hoping to receive a last-minute offer, including Minnesota defensive end Ray Edwards. Meanwhile, four Green Bay starters -- defensive end Johnny Jolly, cornerback Tramon Williams, safety Atari Bigby and guard Daryn Colledge -- are still available.
If they don't sign their offer sheet by April 15, then they can't sign with another team (which they haven't been able to do over the last month anyway) and they must sign by June 15. That's not much of a deadline. So if you've heard about the it and wondered if it's a big deal: it isn't. All it means is that the players go from a "95 percent chance" they'll be back with the Packers to a 100% chance. There is little incentive for the players to sign by April 15, and they actually lose some leverage to negotiate a long-term contract.