Meanings of Symbols

So I was thinking today, about symbols. I blame Dan Brown. Intermingled with his fiction writing, there is a great analysis of symbols and their meaning. So I started thinking about symbols and their meanings. They literally do not mean anything until humanity decides to add significance to them.
Is not a flag simply a piece of fabric until you assign meaning to it? If you take the meaning from it, is it not simply a piece of fabric once again?
Is not a series of lines, just a series of lines until you decide that it is representative of a group, organization, or event?
Is not a cross simply perpendicular lines until you ask a Christian about its meaning?

Is a Star of David simply two triangles overlapping until you ask a Jew?

Is a crescent moon with a star simply celestial representations until you ask a Muslim?

I do not mean to say that there is no significance to these things. I mean simply that it is not the symbol itself that is important. But the meaning behind it.