I suggest calling the police hotline found on
http://www.spf.gov.sg/ (Police Hotline 1800 - 255 0000) to verify
the authencity of the note. For all you know, the "IO" might be a
fake and is trying to pull a scam. Eitherway, if the note is real,
you don't have to worry if you done nothing wrong. If it is proven
to be fake however, do make a police report as soon as
possible.