Signs and Symbols

I was kind of wondering of how these signs and symbol came to life. Obviously there goes a rich history of this and much more is written about it compared to what I may be saying.
This point came to my mind when I was looking at different icons on my laptop. So I should rather be saying how the symbols/icons in the software came to existence and why of particular shape and colour. Even today they are not changed much. Why so? Exploring my laptop desktop and open applications the "X" sign caught my attention.

These red crossed thing is used everywhere in software to indicate "close/exit/error" in the system. I didn't know why. Why is red color associated with something that is wrong or going to exit/end in software applications. May be it's not like that in other Operating systems or software applications. But this is the most used one. To explore more I went to Wikipedia and found information on different types of crosses prevalent across world, but with religion in perspective (http://en.wikipedia.org/wiki/Category:Cross_symbols).

And then this came before me http://www.guidebookgallery.org/icons/components
A very good link showing different types of icons in different Operating systems that too with year. So in one screen we get an idea of how these icons have evolved. Though it has not answered my query as of now, I'm ending my note here 'coz of time limit. I'll be searching for it though.