Where are you going to start? And how much are people willing to pay for increased safety? Many of the people who voice fear over safety concerns would be the first ones to complain about the increased costs of making Thailand safer. To achieve basic safety, you'll need to do a lot more retroactively than raise signs. You'll also need to:
* increase the height of balustrades
* maintain crosswalks and police them
* enforce laws against scooters riding against the direction of traffic
* maintain safety standards and inspections (remember the people killed in hotels a few years ago by bug bombs?)
Oh, why go on? The list is a mile long. But the point is, if you want all this stuff, you're going to need to pay for it. Who is the first to sign up for their taxes and fees to be increased?