Square, Circle, Trangle: Train Style

Just a few images I have collected from my train rides to and from Banbury. Its mostly signage but it has shown me that there is a correlation between colours, both primary and secondary, an these three shapes.

Yellow triangular warning sign.

Red circular no smoking sign.

More yellow triangular warning signs.

Yellow circular button cases.

Blue and white circular litter sign.

Another yellow triangular warning sign.

Some kind of weird bolt that shows a mixture of circles and squares. I have noticed most train staff carry a T-Wrench that will fit in to this slot, I'm guessing to release a door. I have noticed the use of primary colours is to grab our attention to the signs and the meanings behind them.