Sharps back with Millers
The 31-year-old had four years with the Millers before bowing out after the League Two play-off final defeat to Dagenham and Redbridge in 2010.
Subject to a medical, he arrives fresh from a promotion-winning campaign with Shrewsbury Town and has signed a two-year contract.
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Hide AdManager Steve Evans said: "It has taken a long time to get Ian here.
"He has had a fantastic two years at Shrewsbury. He is someone we admire and respect and I am looking forward to seeing him in action."
Sharps joins forwards Daniel Nardiello and Kayode Odejayi as the Millers' new signings, with more expected by the end of the week.