Icons are signs whose signifier bears a close resemblance to the thing to which they refer
Icons are said to be motivated
Iconic signs have a marked physical or perceptual resemblance between the signifier and that to which they refer
Words are symbolic signs
There is no natural relationship between the word and its meaning, it's abitary and meanings are arrived at by a cultural convention.
Pierce used the word symbol to refer to a category of sign when there is no resemblance between it and its object.
Indexes lie somewhere in between icons and symbols. An index is a sign whose signifier we have learnt to identify with a particulare signified.
An index is connected to its object.
e.g. smoke is an index of fire
Icons, symbols and indexes are INTERACTIVE and OVERLAPPING