"Gotta silence the lambs, get on my Buffalo Bill!" Spikes wrote on his Twitter account. "#51 #BILLSMAFIA taking back the #AFCEAST #PoWwWwW."
Spikes recorded 86 tackles and an interception last season.
Meanwhile, the Bills are signing free agent running back Anthony Dixon.
Dixon rushed for 458 yards and eight touchdowns in four seasons for the 49ers.
"So glad to be the newest member of the Buffalo Bills," Dixon wrote on Twitter. "gonna make this thang offficial in the morning."
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Aaron Wilson covers the Ravens for The Baltimore Sun