After two apparent homicides in 24 hours, Mayor Linda Balzotti is asking residents to be vigilant and to become part of the solution. In a statement posted on the city’s website, Balzotti asked residents to join neighborhood watches and report tips to the police department. Tips can be sent through the Brockton Police Community Education Facebook page, via text at “CRIMES” or 274637, texting Tip709 at the beginning of the message, or by phone at 508-941-0244. “Please know we continue to take a zero-tolerance approach to crime in Brockton,’’ Balzotti said. “Now more than ever, I am asking all residents and business owners to stand together, in unity, against violence in our city.” There have been nine homicides in the city this year, three more than in all of 2012.