A few residents of Tampines Blk 417 told me that last week, a man claiming to be instructed by me, had knocked on their doors (once even at midnight). He asked to enter their homes to check on something. Rightfully, they were suspicious and did not oblige. According to the description, the man looks to be in his thirties and has shoulder-length hair.
Anyone from the town council or any public agency should be in uniform and able to produce proof of identity (eg card with photo and official logo). Grassroots leaders, being volunteers, would not have any official ID. However, they would not be asking to enter your homes or for confidential information (eg NRIC no). When in doubt, call the police.