But didn't someone suggest that terrorism isn't a big threat?

Note the snippet here about extremely heavy security at the UN climate change conference in Bali:

Bali's police spokesman A.S. Reniban said that 8,000 military personnel and 8,000 police officers were stationed near the conference centre, in addition to the UN police force patrolling the summit grounds.

I wonder if they considered just posting signs saying "Terrorism banned on these premises".