Lookout Linkage, 2/17/15

Links!

• The Dodgers have signed former Mariners' closer David Aardsma to a minor league contract.
• The Yankees will retire the numbers of three players this summer.
• Nick Schwartz of USA Today wonders when the Yankees will run out of numbers to retire (it isn't as soon as you think).
• Jeff Zimmerman of The Hardball Times wonders if WAR is a fair measurement of pitchers' success.
• Sean Dolinar of Fangraphs analyzes the Twitter usage of each MLB team over the course of the offseason.
• Jason Giambi has officially retired from Major League Baseball.
• The A's have signed pitcher Barry Zito to a minor league deal.
• Garrett Richards has thrown his first bullpen session since his surgery.