With the cross, it's simply to say that Jesus died on the cross in order for our sins to be forgiven
With the fish, at one point Christianity was outlawed in Rome, and so Christians created the symbol to communicate and show they were Christians.
This was a good choice for a few reasons. For starters, this was easily drawable; they would take a piece of paper, sketch the fish on it with chalk, and they knew they could trust each other. The actual reason it was chosen for the design, if I remember correctly, is because of Jesus breaking the loaves of bread, and tearing the fish, and giving the pieces to 5,000 men, and later on 4,000 (vise versa).
Which one as there are many used by people to denote their Christian affiliation. Consider the crucifix, crown of thorns, fish, dove, fire, etc... They come in jewelry, statues, paintings, nicknacks, etc...
Additional Comments:
Tomorrow, most Roman Catholic, Anglican and Eastern Orthodox members will go to their local church and receive an outward sign of a 'thumb print' of ash on their foreheads indicating they recognize the start of Lent - a day of penitence to clean the 'soul' before the 40 day lenten fast. See related link below:
It's an early Christian symbol (if that's what you mean, the question is a bit unclear for me). It is supposed to signify Christ.
They are the Greek symbol for Christ, although most Christian groups also use it.
There is no way to answer your question unless you tell us what the symbol is. Do you mean a cross? Or perhaps a fish symbol? Please clarify your question.
The Cross of St. Peter or Petrine Cross is an inverted Latin cross traditionally used as a Christian symbol, but in recent times also used widely as an anti-Christ symbol (a meaning which is not valid with respect to traditional conventions of Christian symbolism).
"Holy cross" or "saint cross" meaning the Christian symbol of the crucifixion of Christ.
Usually the dove is the symbol of peace
The Christian Cross is a religious symbol.
No.
brown
The sacrament or rite of ordination as a member of the Christian clergy, esp. in the grades of bishop, priest, or deacon.
Neither.
It's the Christian "fish" symbol.