the top part
is a hand holding a brush, the bottom is a flat writing material. It shows that a person is writing with a brush. Another explanation is that the bottom is character Mouth, which means that a person uses brush to "speak" something. "Speak" here is same as "Express".
Its small seal script is
Its clerical script is
similar to the small seal script, a little bit simpler. We can see five fingers - the five horizontal lines, the brush - the vertical line, and paper - the bottom part.
Its current standard printing script for traditional character is
same as the clerical script.
Its current standard printing script for simplified character is
changed dramatically, not pictography any more. This is another example that the simplified character destroyed the pictography.
I need to point out that the 书 is used more often for its another meaning "Book". The original "Write" meaning is used less popular. But the character was created as "Write", not "Book". Book is the product of writing, so people used the same character to mean "Book".
Its Pinyin is "Shu1".