What is the term for a sign that has no necessary or natural connection to the thing it stands for or signifies?

The term for a sign that has no necessary or natural connection to the thing it represents is "arbitrary sign." In semiotics, this concept highlights that the relationship between the signifier (the sign itself) and the signified (the concept it represents) is based on social convention rather than any intrinsic link. Language and symbols often fall into this category, as their meanings are assigned rather than inherently obvious.