Depending on where you see them, thorns may have many meanings. If placed on a rose, it may indicate a beauty that can be seen, but never touched; placed upon a cross, they have religious significance; all by themselves, they are a symbol of self defense, self preservation, and overall protection from those who might hurt us. People may get thorn tattoos for these reasons, but much more often they are used because they simply look dangerous, and add a bit of toughness to any piece they end up in.
The vast majority of thorn tattoos are used in armband pieces. They are usually very simple, and are wrapped around the upper arm; however, they may also be seen wrapped around a wrist, ankle, or even the waist of the wearer. Many people like to use a tribal style, but you may also occasionally see realistic brown thorns. Thorns made of metal or gold; have small flower blossoms, or surrounded in fire are seen less frequently, but make for a more unique feel.
Some thorn tattoos are based in religion. The sacred heart (which is wrapped in thorns), or a crown of thorns (either set upon Jesus Christ’s head, or on its own) are two great examples. For a more unusual religiously-based piece you could create a cross with a crown of thorns placed around the top; a dove making a nest of thorns; or even shape the thorns themselves into the shape of the sacred heart. This could be done in a patch style, or even as an armband.
Quite a few thorn tattoos are meshed together with symbols that are generally considered to be more romantic. For instance, you may see a thorn pressing through a heart, which is often used as an alternative to the classic broken heart. A cartoon-styled heart may be wrapped all around with thorns to symbolize a guarded heart. A rose with a thorn, of course, states untouchable beauty; however, a stem covered entirely in thorns may be used to indicate a sense of protection. For a different take on this, you could create a bush of thorns with a single, bright red rose blossoming from it; or simply wrap the rose around the thorn. You might also mingle the two themes, and wrap a rose around a heart, with thorns attaching the two together.
There are many ways to use thorn tattoos as either a main piece, or simply an enhancement to a much broader theme. Either way, you will be adding a certain sense of protection, toughness and strength to your piece with these small, often painful symbols.