The penalties for creating graffiti in Singapore include caning:You're right about that but I have never seen or heard the Singapore MRT getting bombed. One thing the penalties are severe in SG if you get caught. Most likely those who will attempt to paint the MRT are die-hard writers from other countries instead of local Singaporeans.
But neighbouring Malaysia had some bombed trains
*Images removed by Mod*
The above images have appeared on several different websites. Sometimes they are purported to be in Singapore and other times in Malaysia.