Following the kidnap of Christian Democracy politician Aldo Moro by the far-left terrorist group the Red Brigades (Brigate Rosse, BR) in March 1978, Signorile became involved in clandestine attempts to develop lines of communication between his party and BR, with the intention of securing Moro's release.

Although always remaining within the confines of the law, Signorile contacted Marxist intellectuals sympathetic to BR, most notably Franco Piperno and Lanfranco Pace, and reported the outcomes of their discussions to the then leader of the PSI, Bettino Craxi.

He was accused together with his secretary Rocco Trane of having received bribes for 720 million lire for the award of a contract for the supply of linen destined for the sleeping cars of Ferrovie dello Stato, was indicted and subsequently acquitted in 1996.

[3] In 2004, Signorile founded the Socialist Unity movement,[4] while in 2005 he joined the new radical-socialist project "Rose in the Fist".

In 2007, he joined the Reformist Alliance of Ottaviano Del Turco, to promote the participation of a group of socialists in the constituent phase of the Democratic Party.