Dragons and serpents do not necessarily symbolize evil. In fact, they mean different things in different cultures so we must be careful not to rush to judgment when we see someone wearing jewelry or t-shirts sporting these symbols.
For instance, the Chinese dragon symbolizes an alleged cosmic energy force known as "chi" and is believed to be a symbol of good fortune. Other cultures revere the dragon as a symbol of strength, courage, power, longevity, and protection, find more details here about everything you need to know about jewelry.
The serpent is another symbol that Christians are inclined to view as a symbol of evil, but this too has different meanings in other cultures. In early Egyptian society it was the symbol of royalty and deity; in other eras and other cultures it has been known to represent eternal love, healing, fertility, wisdom, and even immortality. These other meanings can also be found in Western cultures which is evidenced by the story of Prince Albert who, in 1840, gave his future bride, Queen Victoria, an engagement that depicted two entwined snakes which were said to demonstrate the mutual love they felt for each other. She is said to have loved the ring so much she was buried in it.
Even the proverbial skull and crossbones symbol has a variety of meanings. For instance, it was one of several symbols used in Medieval and Renaissance art to depict death and mortality. The skull was also known to be a frequent companion of many Christian saints who looked upon it as a reminder of the certainty of death and the need to reject the fleeting material world. This is why we often see it depicted in Christian art, sometimes paired with a book as a symbol of studiousness.
Believe it or not, even the pentagram, a traditional symbol of evil, has other meanings in other cultures. A Greek word meaning "five lines", depending on the way the pentagram is drawn, it has been used as symbol for everything from the five wounds of Jesus to Satanic power.
There are just too many reasons why someone would show up in church in a dragon t-shirt and serpent earrings. As bizarre as it may look to some, the person may be wearing it simply because they think it looks cool.
The bottom line is that it's probably not a good idea to judge a person just by the jewelry or symbols they're wearing!