The only way that I know of to get the answers you are looking for would be to interview some bikers or ex bikers, but be careful about approaching them- you can try to find some in a recovery program or through a community outreach program (they like helping kids). Frankly, there really aren't many tattoos, that I know of anyway, that "mean" anything to bikers- they put more emphasis on their vests & jackets to carry symbols than on their skin.  You would have been FAR better off to have picked gang tattoos, or better yet, prison tattoos.  If there's ANY way to alter the topic, I would really suggest you do it- there will be far more information on those other subjects because tattoos are used to effect messages far more frequently among gangs inside and outside of prisons.  There's at least one book on Russian prison tattoos and there are innumerable sources of information on gang and prison tattoo in the US- including the prison systems, local law enforcement gang task forces, the US Justice Department and the FBI.
I can give you a little of an overview if you are able to change your topic.  Otherwise, I can't help you much except to tell you that biker's SOMETINES get 1%er tattoos and will OCCAISIONALLY get tear drps tattooed under their eyes.

1%er tattoos are the same thing as a 1%er patch on their vests-  Here's a quote from a biker terminology page that gives a very accurate explanation of what the 1% patch or tattoo is- among hard core bikers like the Bandidos (from personal experience) this is a covetewd title and not one to be worn without having been 'authorized' to do so:

"1%er = If you read the papers or listen to the news, the media and law enforcement agents have redefined the term "1%er". The term was first used in the 60's to describe some of the people that attended the motorcycle events back then. The AMA (American Motorcycle Association) stated that 99% of the people at their events were god fearing and family oriented. The other 1%er were hard riding, hard partying, non mainstream type people. Thus the term 1%er was born. Some of the early bikers embraced the term and decided to call themselves 1%ers.  It did not mean that they were law breakers or low life individuals. They were simply men that rode their motorcycles seven days a week in all kinds of weather, liked to drink and raise a little hell. Sometime during the 80's law enforcement changed the meaning of the 1%er to what they wanted it to represent. It didn't matter that their meaning was incorrect, they just spoon fed it to the general public and the courts as they had so many other things.

Motorcycle Clubs are rich in history and tradition. One of those traditions is the wearing of a 1%er patch on our vests and referring to ourselves as a 1%er club. The 1%er definition as we see it is one that explains our commitment to Biking and Brotherhood. We ride our motorcycles every day rain or shine. We ride thousands of miles each year with our Brothers to attend parties, social events, funerals and just plain spending time together. We work, have families and do all the things that our neighbors do. In addition to that we belong to a Brotherhood that we are able to combine with our day to day lives.  To say that 1%er's are criminals or people of a lesser moral code than the rest of society is a tainted opinion."

Teardrop tattoos- Teardrops mean a variety of things- it depends on the person wearing them and the gang or group.  They can mean anything from the fact that the wearer has killed someone to the fact that they've lost a family member or fellow gang member.  Depending on the meaning and the particular group, the teardrop may, or may not, be filled in- what means one thing to one person may mean something totally different to someone else.  What matters as much, or more than the tattoo, is the context that it's worn in.