Daggers have been a popular tattoo design especially within the last 60 or so years. There is often not a lot of meaning attached to these tattoos and they are considered to be mainly decorative. However, there is a surprising amount of symbolism attached to the dagger.
Daggers are mainly representative of death, or more specifically, death caused by another person. It is also symbolic of ferocity and deadliness in general.
In the past a dagger dripping with blood was a message to others that the wearer had a concealed weapon and that they would use it if they had to. Due to this, a dripping dagger in modern times can be used to represent someone who is fearless and not willing to back down if confronted by someone who opposes them (not necessarily in a violent way although there are obvious connotations of violence attached with the dagger imagery).
A dagger and skull design can further illustrate the representation of death. A dagger through a heart can represent being betrayed by a boyfriend, girlfriend or spouse for example and serve as a reminder to not make the same mistakes again.
You may also see daggers in the teeth of skulls and some other designs. This theme was popularized in old pirate films when the pirates would board the enemy ship by swinging from a rope while holding their sword or dagger in their teeth. This type of design therefore represents readiness and ferocity, but also just pirate.
The last common type of dagger design is a dagger going either into the skin or in and out again. This design is mainly used to symbolize being wounded by something or someone at some point in your life, which I’m sure everyone can relate to, and is therefore a popular tattoo design.