Municipal retirement officials on Monday will discuss the recent guilty plea of a retired police sergeant who has been collecting his departmental pension for 18 months. Joseph Deignan, 58, of Framingham, pleaded guilty Tuesday in federal court to stealing an ID while on the force, and using it to obtain oxycodone and other prescription drugs, according to the office of US Attorney Carmen Ortiz. He was charged with unlawful possession of a controlled substance by fraud, and fraud in connection with identification documents, the prosecutor’s office said. Federal authorities said that Deignan had stolen a driver’s license while working as a traffic supervisor in 2010 and used it to obtain forged prescriptions. Watertown retirement officials said Deignan, who served on the department for 32 years, has been collecting an annual pension of $55,731 since his retirement in February 2012. The board will discuss further actions during its 8:30 a.m. meeting in Town Hall . The discussion of Deignan will be mostly informational, said the Watertown Contributory Retirement System’s director, Barbara Sheehan. Officials will likely talk about obtaining court documents and decide whether they want to call Deignan in for a hearing, she said.