Someone was claiming that a warning from the police counted as a criminal record (but that it could be countered), and people were also talking a lot of nonsense in forums, so here's a definitive answer:

"A stern warning means the person will not have a criminal record, but it can be taken into account by police if he repeats the offence."

--- The Straits Times, Friday, October 7, 2005 / Leslie Koh (via Access World News)