Anyway if you still think they don't have the right to check your bag. This was a true case that happened a few month back. Anyway this thread was from a thread at hardwarezone and I can't seem to find it now.
To summarise,
1. There will be two person, A and B
2. B jio A to come down to A's void deck to vape together
3. A brought down his mod and some juice and while B was waiting for A, B put his mod on the void deck table
4. A met B and they started talking. At this point, A have not taken out his vape gear from his bag while B's mod is still sitting on the table
5. Suay suay a group of police (or was it HiShAm?) was walking by the void deck and spotted B's mod
6. Approached the two (A and B) and confiscated B's mod (Don't know if any fine was involved)
7. With reasonable suspicion, the officers (either police or HiShAm, I don't remember) asked to check A's bag
8. Officers found the mod and juice in A's bag and confiscated them.
It's the same for travelling also. SMRT personnel have the authority to check your bag. That's why there's a security counter in MRT. If they find out about your vape gear, they do not have the right to confiscate it. But they will hold you and call the relevant authorities to deal with you.
