Symbols can change in meanings overtime, they can start to mean something than what they first intentionally were used for. They symbols meaning changes as society sees the imagery differently.
For example, what we know today, for the Poison Sign, was originally a different symbol.
Above is Today’s symbol for poison, but it was originally derived from the era of pirates, used as a warning sign as well as caution. Below shows the pirates flag with the same skull and bones symbol.