这样如何？

请不要把菸灰弹入此处! 

Cigarette Ash Forbidden

应该是：No Cigarette Ash

小心地滑

Slippery Floor

应该是：Watch out, flippery floor

关怀弱势儿童

Care for Disadvantaged Children

应该是：Show your love and care for those less fortunate children.

不可回收

Non-Recyclable

文明机场

Airport of Superb Service

老弱病残孕」的坐椅  （on bus)

Seat for Disabled

当心碰头

Mind Your Head

应该是：Watch for xxx, e.g. overhead bar.